9394949438

[LATEST]$type=sticky$show=home$rm=0$va=0$count=4$va=0

NCERT Solutions for Class 8 Maths Chapter 9 Algebraic Expressions and Identities

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.1 what are expressions?

Question: 1 Give five examples of expressions containing one variable and five examples of expressions containing two variables.

Answer:

Five examples of expressions containing one variable are:

x^{^{4}}, y, 3z, p^{^{2}}, -2q^{3}

Five examples of expressions containing two variables are:

x + y, 3p-4q,ab,uv^{2},-z^{2}+x^{3}

Question: 2(i) Show on the number line :

x

Answer:

x on the number line:

Question: 2(ii) Show on the number line :

x-4

Answer:

x-4 on the number line:

Question: 2(iii) Show on the number line :

2x+1

Answer:

2x+1 on the number line:

Question: 2(iv) Show on the number line:

3x-2

Answer:

3x - 2 on the number line

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.2 terms, factors and coefficients

Question:1 Identify the coefficient of each term in the expression.

x^2y^2-10x^2y+5xy^2-20

Answer:

coefficient of each term are given below

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.3 monomials, binomials and polynomials

Question: 1(i) Classify the following polynomials as monomials, binomials, trinomials.

-z+5

Answer:

Binomial since there are two terms with non zero coefficients.

Question: 1(ii) Classify the following polynomials as monomials, binomials, trinomials.

x+y+z

Answer:

Trinomial since there are three terms with non zero coefficients.

Question:1(iii) Classify the following polynomials as monomials, binomials, trinomials.

y+z+100

Answer:

Trinomial since there are three terms with non zero coefficients.

Question: 1(iv) Classify the following polynomials as monomials, binomials, trinomials.

ab-ac

Answer:

Binomial since there are two terms with non zero coefficients.

Question: 1(v) Classify the following polynomials as monomials, binomials, trinomials.

17

Answer:

Monomial since there is only one term.

Question: 2(a) Construct 3 binomials with only x as a variable;

Answer:

Three binomials with the only x as a variable are:

\\ \\x+2,\ x +x^{2},\ 3x^{3}-5x^{4}

Question: 2(b) Construct 3 binomials with x and y as variables;

Answer:

Three binomials with x and y as variables are:

\\ \\x+y,\ x-7y, xy^{2} + 2xy

Question: 2(c) Construct 3 monomials with x and y as variables;

Answer:

Three monomials with x and y as variables are

\\ xy,\ 3xy^{4},\ -2x^{3}y^{2}

Question: 2(d) Construct 2 polynomials with 4 or more terms .

Answer:

Two polynomials with 4 or more terms are:

a+b+c+d, x-3xy+2y+4xy^{2}

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.4 like and unlike terms

Question:(i) Write two terms which are like

7xy

Answer:

\\Two\ terms\ like\ 7xy\ are:\\ -3xy\ and\ 5xy

Question:(ii) Write two terms which are like

4mn^2

Answer:

\\Two\ terms\ which\ are\ like\ 4mn^{2}\ are:\\ mn^{2}\ and -3mn^{2.}

we can write more like terms

Question:(iii) Write two terms which are like

2l

Answer:

\\Two\ terms\ which\ are\ like\ 2l\ are:\\ l\ and\ -3l

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities-Exercise: 9.1

Question:1(i) Identify the terms, their coefficients for each of the following expressions.

5xyz^2-3zy

Answer

following are the terms and coefficient

The terms are 5xyz^{2}\ and\ -3zy and the coefficients are 5 and -3.

Question: 1(ii) Identify the terms, their coefficients for each of the following expressions.

1+x+x^2

Answer:

the following is the solution

\\The\ terms\ are\ 1,\ x,\ and\ x^{2}\ and\ the\ coefficients\ are\ 1,\ 1,\ and\ 1\ respectively.

Question:1(iii) Identify the terms, their coefficients for each of the following expressions.

4x^2y^2-4x^2y^2z^2+z^2

Answer:

Question: 1(iv) Identify the terms, their coefficients for each of the following expressions.

3-pq+qr-rp

Answer:

The terms are 3, -pq, qr,and -rp and the coefficients are 3, -1, 1 and -1 respectively.

Question:1(v) Identify the terms, their coefficients for each of the following expressions.

\frac{x}{2}+\frac{y}{2}-xy

Answer:

Above are the terms and coefficients

Question: 1(vi) Identify the terms, their coefficients for each of the following expressions.

0.3a-0.6ab+0.5b

Answer:

The terms are 0.3a, -0.6ab and 0.5b and the coefficients are 0.3, -0.6 and 0.5.

Question: 2(a) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

x+y

Answer:

Binomial.

Question: 2(b) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

1000

Answer:

Monomial.

Question: 2(c) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

x+x^2+x^3+x^4

Answer:

This polynomial does not fit in any of these three categories.

Question: 2(d) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

7+y-5x

Answer:

Trinomial.

Question: 2(e) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

2y-3y^2

Answer:

Binomial.

Question: 2(f) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

2y-3y^2+4y^3

Answer:

Trinomial.

Question: 2(g) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

5x-4y+3xy

Answer:

Trinomial.

Question: 2(h) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

4z-15z^2

Answer:

Binomial.

Question: 2(i) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

ab+bc+cd+da

Answer:

This polynomial does not fit in any of these three categories.

Question:2(j) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

pqr

Answer:

Monomial.

Question: 2(k) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

p^2q+pq^2

Answer:

Binomial.

Question: 2(i) Classify the following polynomials as monomials, binomials, trinomials. Which polynomials do not fit in any of these three categories?

2p+2q

Answer:

Binomial.

Question: 3(i) Add the following.

ab-bc , bc -ca, ca-ab

Answer:

ab-bc+bc-ca+ca-ab=0.

Question:3 (ii) Add the following.

a-b+ab, b-c+bc, c-a+ac

Answer:

\\a-b+ab+b-c+bc+c-a+ac\\ =(a-a)+(b-b)+(c-c)+ab+bc+ac\\ =ab+bc+ca

Question:3 (iii) Add the following

2p^2q^2-3pq+4, 5+7pq-3p^2q^2

Answer:

\\2p^{2}q^{2}-3pq+4+5+7pq-3p^{2}q^{2}\\ =(2-3)p^{2}q^{2} +(-3+7)pq +4+5\\ =-p^{2}q^{2}+4pq+9

Question: 3(iv) Add the following.

l^2+m^2+n^2 , n^2+l^2, 2lm+2mn+2nl

Answer:

\\l^{2}+m^{2}+n^{2}+n^{2}+l^{2}+2lm+2mn+2nl\\ =2l^{2}+m^{2}+2n^{2}+2lm+2mn+2nl

Question: 4(a) Subtract 4a-7ab+3b+12 from 12a-9ab+5b-3

Answer:

12a-9ab+5b-3-(4a-7ab+3b+12)
=(12-4)a +(-9+7)ab+(5-3)b +(-3-12)
=8a-2ab+2b-15

Question: 4(b) Subtract 3xy+5yz-7zx from 5xy-2yz-2zx+10xyz

Answer:

\\5xy-2yz-2zx+10xyz-(3xy+5yz-7zx)\\ =(5-3)xy+(-2-5)yz+(-2+7)zx+10xyz\\ =2xy-7yz+5zx+10xyz

Question: 4(c) Subtract 4p^2q - 3pq + 5pq^2 - 8p + 7q - 10 from 18 - 3p - 11q + 5pq - 2pq^2 + 5p^2q

Answer:

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.7.2 multiplying three or more monomials

Question:1 Find 4x\times 5y\times 7z . First find 4x\times 5y and multiply it by 7z ; or first find 5y \times 7z and multiply it by 4x .

Answer:

We observe that the result is same in both cases and the result does not depend on the order in which multiplication has been carried out.

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities-Exercise: 9.2

Question: 1(i) Find the product of the following pairs of monomials.

4,7p

Answer:

4\times 7p=28p

Question: 1(ii) Find the product of the following pairs of monomials.

-4p,7p

Answer:

<img alt="\\-4p\times 7p\\=(-4\times 7)p\times p\\=-28p^{2}" height="61"

src="https://lh3.googleusercontent.com/ZQLwJFEoi48QnxUuK79XbVO1Ug-ZvBoOflH3wFRfnzdHsH_uWOVnOwg4kaF8g0o8RSXTEfDcwrA7mDeS0UuxfpygL0vqvj2Ip_Ntb3J0UEOs2WBYddLAm3Ff_WG8HAzyPrqB_V0" style="margin-left: 0px; margin-top: 0px;" width="128" />

Question: 1(iii) Find the product of the following pairs of monomials

-4p,7pq

Answer:

-4p\times 7pq\\=(-4\times 7)p\times pq\\=-28p^{2}q

Question: 1(iv) Find the product of the following pairs of monomials.

4p^3,-3p

Answer:

\\4p^{3}\times (-3p)\\ =4\times (-3)p^{3}\times p\\=-12p^{4}

Question:1(v) Find the product of the following pairs of monomials.

4p,0

Answer:

\\4p\times 0=0

Question:2(A) Find the areas of rectangles with the following pairs of monomials as their lengths and breadths respectively.

(p,q)

Answer:

The question can be solved as follows

\\Area=length\times breadth\\ =(p\times q)\\ =pq

Question:2(B) Find the areas of rectangles with the following pairs of monomials as their lengths and breadth respectively.

(10m,5n)

Answer:

the area is calculated as follows

\\Area=length\times breadth\\ =10m\times 5n\\ =50mn

Question:2(C) Find the areas of rectangles with the following pairs of monomials as their lengths and breadths respectively.

(20x^2,5y^2)

Answer:

the following is the solution

\\Area=length\times breadth\\ =20x^{2}\times 5y^{2}\\ =100x^{2}y^{2}

Question:2(D) Find the areas of rectangles with the following pairs of monomials as their lengths and breadths respectively.

(4x,3x^2)

Answer:

area of rectangles is

\\Area=length\times breadth\\ =4x\times 3x^{2}\\ =12x^{3}

Question:2(E) Find the areas of rectangles with the following pairs of monomials as their lengths and breadths respectively.

(3mn,4np)

Answer:

The area is calculated as follows

\\Area=length\times breadth\\ =3mn\times 4np\\ =12mn^{2}p

Question:3 Complete the table of products.

First monomial \rightarrow


Second monomial \downarrow

2x

-5y

3x^2

-4xy

7x^2y

-9x^2y^2

2x

4x^2

...

...

...

...

...

-5y

...

...

-15x^2y

...

...

...

3x^2

...

...

...

...

...

...

-4xy

...

...

...

...

...

...

7x^2y

...

...

...

...

...

...

-9x^2y^2

...

...

...

...

...

...

Answer:

First monomial \rightarrow


Second monomial \downarrow

2x

-5y

3x^{2}

-4xy

7x^{2}y

-9x^{2}y^{2}

2x

4x^{2}

-10xy

6x^{3}

-8x^{2}y

14x^{3}y

-18x^{3}y^{2}

-5y

-10xy

25y^{2}

-15x^{2}y

20xy^{2}

-35x^{2}y^{2}

45x^{2}y^{3}

3x^{2}

6x^{3}

-15x^{2}y^{}

9x^{4}

-12x^{3}y

21x^{4}y

-27x^{4}y^{2}

-4xy

-8x^{2}y

20xy^{2}

-12x^{3}y

16x^{2}y^{2}

-28x^{3}y

36x^{3}y^{3}

7x^{2}y

14x^{3}y

-35x^{2}y^{2}

21x^{4}y

-28x^{3}y^{2}

49x^{4}y^{2}

-63x^{4}y^{3}

-9x^{2}y^{2}

-18x^{3}y^{2}

45x^{2}y^{3}

-27x^{4}y^{2}

36x^{3}y^{3}

-63x^{4}y^{3}

81x^{4}y^{4}

Question:4(i) Obtain the volume of rectangular boxes with the following length, breadth and height respectively.

5a, 3a^2, 7a^4

Answer:

\\Volume=length\times breadth\times height\\ =5a\times 3a^{2}\times 7a^{4}\\ =15a^{3}\times 7a^{4}\\ =105a^{7}

Question:4(ii) Obtain the volume of rectangular boxes with the following length, breadth and height respectively.

2p,4q,8r

Answer:

the volume of rectangular boxes with the following length, breadth and height is

\\Volume=length\times breadth\times height\\ =2p\times 4q\times 8r\\ =8pq\times 8r\\ =64pqr

Question:4(iii) Obtain the volume of rectangular boxes with the following length, breadth and height respectively.

xy, 2x^2y, 2xy^2

Answer:

the volume of rectangular boxes with the following length, breadth and height is

Question:4(iv) Obtain the volume of rectangular boxes with the following length, breadth and height respectively.

a, 2b, 3c

Answer:

the volume of rectangular boxes with the following length, breadth and height is

\\Volume=length\times breadth\times height\\ =a\times 2b\times 3c\\ =2ab\times 3c\\ =6abc

Question:5(i) Obtain the product of

xy,yz,zx

Answer:

the product

\\xy\times yz\times zx\\ =xy^{2}z\times zx\\ =x^{2}y^{2}z^{2}

Question:5(ii) Obtain the product of

a,-a^2,a^3

Answer:

the product

\\a\times (-a^{2})\times a^{3}\\ =-a^{^{3}}\times a^{3} =-a^{6}

Question:5(iii) Obtain the product of

2,\ 4y,\ 8y^{2},\ 16y^{3}

Answer:

the product

\\2\times 4y\times 8y^{2}\times 16y^{3}\\ =8y\times 8y^{2}\times 16y^{3}\\ =64y^{3}\times 16y^{3}\\ =1024y^{6}

Question:5(iv) Obtain the product of

a, 2b, 3c, 6abc

Answer:

the product

\\a\times 2b\times 3c\times 6abc\\ =2ab\times 3c\times 6abc\\ =6abc\times 6abc\\ =36a^{2}b^{2}c^{2}

Question:5(v) Obtain the product of

m, -mn, mnp

Answer:

the product

\\m\times (-mn)\times mnp\\ =-m^{2}n\times mnp\\ =-m^{3}n^{2}p

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.8.1 multiplying a monomial by a binomial

Question:(i) Find the product

2x(3x+5xy)

Answer:

Using distributive law,

2x(3x + 5xy) = 6x^2 + 10x^2y

Question:(ii) Find the product

a^2(2ab-5c)

Answer:

Using distributive law,

We have : a^2(2ab-5c) = 2a^3b - 5a^2c

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.8.2 multiplying a monomial by a trinomial

Question:1 Find the product:

(4p^2+5p+7)\times 3p

Answer:

By using distributive law,

(4p^2+5p+7)\times 3p = 12p^3 + 15p^2 + 21p

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities-Exercise: 9.3

Question:1(i) Carry out the multiplication of the expressions in each of the following pairs.

4p, q+r

Answer:

Multiplication of the given expression gives :

By distributive law,

(4p)(q+r) = 4pq + 4pr

Question:1(ii) Carry out the multiplication of the expressions in each of the following pairs.

ab, a-b

Answer:

We have ab, (a-b).

Using distributive law we get,

ab(a-b) = a^2b - ab^2

Question:1(iii) Carry out the multiplication of the expressions in each of the following pairs.

a+b, 7a^2b^2

Answer:

Using distributive law we can obtain multiplication of given expression:

<img alt="(a + b)(7a^2b^2) = 7a^3b^2 + 7a^2b^3" height="20"

src="https://lh6.googleusercontent.com/zym-v6hoY_4dPgfdHnN35kmtdqAvE_B4CvAHBzx42tg4OdnWGpufkQNURYQP8yq9xk7qpbbNA_sAzgb0gc0AnG0Vxa5aU4snOBR80IU5GQ_6VDoRBqkDdZGjqZfE11JML0vyGTI" style="margin-left: 0px; margin-top: 0px;" width="232" />

Question:1(iv) Carry out the multiplication of the expressions in each of the following pairs.

a^2-9,4a

Answer:

We will obtain multiplication of given expression by using distributive law :

(a^2 - 9 )(4a) = 4a^3 - 36a

Question:1(v) Carry out the multiplication of the expressions in each of the following pairs.

pq+qr+rp, 0

Answer:

Using distributive law :

(pq + qr + rp)(0) = pq(0) + qr(0) + rp(0) = 0

Question:2 Complete the table

First expression

Second expression

Product

(i)

a

b+c+d

...

(ii)

x+y-5

5xy

...

(iii)

p

6p^2-7p+5

...

(iv)

4p^2q^2

p^2-q^2

...

(v)

a+b+c

abc

...

Answer:

We will use distributive law to find product in each case.

First expression

Second expression

Product

(i)

a

b+c+d

ab + ac+ ad

(ii)

x+y-5

5xy

5x^2y + 5xy^2 - 25xy

(iii)

p

6p^2-7p+5

6p^3 - 7p^2 + 5p

(iv)

4p^2q^2

p^2-q^2

4p^4q^2 - 4p^2q^4

(v)

a+b+c

abc

a^2bc + ab^2c + abc^2

Question:3(i) Find the product.

(a^2)\times (2a^{22})\times (4a^{26})

Answer:

Opening brackets :

(a^2)\times (2a^{22})\times (4a^{26}) = (a^2\times2a^{22})\times(4a^{26}) = 2a^{24}\times4a^{26}

or =8a^{50}

Question:3(ii) Find the product.

(\frac{2}{3}xy)\times (\frac{-9}{10}x^2y^2)

Answer:

We have,

(\frac{2}{3}xy)\times (\frac{-9}{10}x^2y^2) = \frac{-3}{5}x^3y^3

Question:3(iii) Find the product.

(\frac{-10}{3}pq^3) \times (\frac{6}{5}p^3q)

Answer:

We have

(\frac{-10}{3}pq^3) \times (\frac{6}{5}p^3q) = -4p^4q^4

Question:3(iv) Find the product.

x \times x^2\times x^3\times x^4

Answer:

We have x \times x^2\times x^3\times x^4

x \times x^2\times x^3\times x^4 = (x \times x^2)\times x^3\times x^4

or (x^3)\times x^3\times x^4

= x^{10}

Question:4(a) Simplify 3x(4x-5)+3 and find its values for

(i) \small x=3

Answer:

(a) We have

3x(4x-5)+3 = 12x^2 - 15x + 3

Put x = 3,

We get : 12(3)^2 - 15(3) + 3 = 12(9) - 45 + 3 = 108 - 42 = 66

Question:4(a) Simplify \small 3x(4x-5)+3 and find its values for

(ii) \small x=\frac{1}{2}

Answer:

We have

\small 3x(4x-5)+3 = 12x^2 -15x + 3

Put

x = \frac{1}{2}

. So We get,

12x^2 -15x + 3 = 12(\frac{1}{2})^2 - 15(\frac{1}{2}) + 3 = 6 - \frac{15}{2} = \frac{-3}{2}

Question:4(b) Simplify \small a(a^2+a+1) + 5 and find its value for

(i) \small a =0

Answer:

We have : \small a(a^2+a+1) +5 = a^3 + a^2 + a +5

Put a = 0 : = 0^3 + 0^2 + 0 + 5 = 5

Question:4(b) Simplify \small a(a^2+a+1)+5 and find its value for

(ii) \small a=1

Answer:

We have \small a(a^2+a+1)+5 = a^3 + a^2 + a + 5

Put a = 1 ,

we get : 1^3 + 1^2 + 1 + 5 = 1 + 1 + 1+ 5 = 8

Question:4(b) Simplify \small a(a^2+a+1)+5 and find its value for

(iii) \small a=-1

Answer:

We have \small a(a^2+a+1)+5 .

or \small a(a^2+a+1)+5 = a^3+a^2+a+5

Put a = (-1)

= (-1)^3+(-1)^2+(-1)+5 = -1 + 1 -1 +5 = 4

Question:5(a) Add: p(p-q),q(q-r) and r(r-p)

Answer:

(a)First we will solve each brackets individually.

p(p-q) = p^2 - pq ; q(q-r) = q^2 - qr ; r(r-p) = r^2 - rp

Addind all we get : p^2 - pq + q^2 - qr + r^2 - rp

= p^2 + q^2 + r^2 -pq-qr-rp

Question:5(b) Add: \small 2x(z-x-y) and \small 2y(z-y-x)

Answer:

Firstly, open the brackets:

\small 2x(z-x-y) = 2xz -2x^2-2xy

and \small 2y(z-y-x) = 2yz-2y^2-2xy

Adding both, we get :

\small 2xz -2x^2-2xy +2yz-2y^2-2xy

or \small = -2x^2-2y^2-4xy + 2xz+2yz

Question:5(c) Subtract: \small 3l(l-4m+5n) from \small 4l(10n-3m+2l)

Answer:

At first we will solve each bracket individually,

\small 3l(l-4m+5n) = 3l^2 - 12lm + 15ln

and \small 4l(10n-3m+2l) = 40ln - 12ml + 8l^2

Subtracting:

\small 40ln - 12ml + 8l^2 - (3l^2 - 12lm+15ln)

or \small = 40ln - 12ml + 8l^2 - 3l^2 + 12lm-15ln

or \small = 25ln + 5l^2

Question:5(d) Subtract: \small 3a(a+b+c)-2b(a-b+c) from \small 4c(-a+b+c)

Answer:

Solving brackets :

3a(a+b+c)-2b(a-b+c) = 3a^2+3ab+3ac - 2ab+2b^2-2bc

= 3a^2+ab+3ac+ 2b^2-2bc

and \small 4c(-a+b+c) = -4ac +4bc + 4c^2

Subtracting : \small -4ac +4bc + 4c^2 -(3a^2 + ab + 3ac+2b^2-2bc)

\small = -4ac + 4bc+4c^2-3a^2-ab-3ac-2b^2+2bc

\small =-3a^2 -2b^2+4c^2-ab+ 6bc-7ac

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities-Exercise: 9.4

Question:1(i) Multiply the binomials.

\small (2x+5) and \small (4x-3)

Answer:

We have (2x + 5) and (4x - 3)
(2x + 5) X (4x - 3) = (2x)(4x) + (2x)(-3) + (5)(4x) + (5)(-3)
= 8 x^{2} - 6x + 20x - 15
= 8 x^{2} + 14x -15

Question:1(ii) Multiply the binomials.

\small (y-8) and \small (3y-4)

Answer:

We need to multiply (y - 8) and (3y - 4)
(y - 8) X (3y - 4) = (y)(3y) + (y)(-4) + (-8)(3y) + (-8)(-4)
= 3 y^{2} - 4y - 24y + 32
= 3 y^{2} - 28y + 32

Question:1(iii) Multiply the binomials

\small (2.5l-0.5m) and \small (2.5l+0.5m)

Answer:

We need to multiply (2.5l - 0.5m) and (2.5l + 0..5m)
(2.5l - 0.5m) X (2.5l + 0..5m) = (2.5l)^{2} - (0.5m)^{2} using (a-b)(a+b) = (a)^{2} - (b)^{2}
= 6.25 l^{2} - 0.25 m^{2}

Question:1(iv) Multiply the binomials.

\small (a+3b) and \small (x+5)

Answer:

(a + 3b) X (x + 5) = (a)(x) + (a)(5) + (3b)(x) + (3b)(5)
= ax + 5a + 3bx + 15b

Question:1(v) Multiply the binomials.

<img alt="\small (2pq+3q^2)" height="19"

src="https://lh4.googleusercontent.com/faqbYXt8AEy2TVr4J1p5vfUz45qyR0d4muq8Xtx5GLLq1Q_3ixfJjPaV3qC_ucxFJnviMKxD4XzZothad36SoNOFM4fgPw4kUMXa3b14Bf5s7YQDTAuZkKh5Nzh92lnwz2Fa810" style="margin-left: 0px; margin-top: 0px;" width="79" /> and \small (3pq-2q^2)

Answer:

(2pq + 3q 2 ) X (3pq - 2q 2 ) = (2pq)(3pq) + (2pq)(-2q 2 ) + ( 3q 2 )(3pq) + (3q 2 )(-2q 2 )
= 6p 2 q 2 - 4pq 3 + 9pq 3 - 6q 4
= 6p 2 q 2 +5pq 3 - 6q 4

Question:1(vi) Multiply the binomials.

\small (\frac{3}{4}a^2+3b^2) and \small 4(a^2-\frac{2}{3}b^2)

Answer:

Multiplication can be done as follows

\small (\frac{3}{4}a^2+3b^2) X \small (4a^2-\frac{8}{3}b^2) = 


3a^{4} - 2a^{2}b^{2} + 12a^{2}b^{2} - 8b^{4}

3a^{4} + 10a^{2}b^{2} - 8b^{4}

Question:2(i) Find the product.

\small (5-2x)\small (3+x)

Answer:

(5 - 2x) X (3 + x) = (5)(3) + (5)(x) +(-2x)(3) + (-2x)(x)
= 15 + 5x - 6x - 2 x^{2}
= 15 - x - 2 x^{2}

Question:2(ii) Find the product.

\small (x+7y)(7x-y)

Answer:

(x + 7y) X (7x - y) = (x)(7x) + (x)(-y) + (7y)(7x) + (7y)(-y)
= 7 x^{2} - xy + 49xy - 7 y^{2}
= 7 x^{2} + 48xy - 7 y^{2}

Question:2(iii) Find the product.

\small (a^2+b)(a+b^2)

Answer:

a^{2} + b) X (a + b^{2} ) = ( a^{2} )(a) + ( a^{2} )( b^{2} ) + (b)(a) + (b)( b^{2} )
a^{3 } + a^{2}b^{2} + ab + b^{3}

Question:2(iv) Find the product.

\small (p^2-q^2)(2p+q)

Answer:

following is the solution

p^{2}- q^{2} ) X (2p + q) = (p^{2})(2p) + (p^{2})(q) + (-q^{2})(2p) + (-q^{2})(q)
2p^{3} + p^{2}q - 2q^{2}p - q^{3}

Question:3(i) Simplify.

\small (x^2-5)(x+5)+25

Answer:

this can be simplified as follows

x^{2} -5) X (x + 5) + 25 = ( x^{2} )(x) + ( x^{2} )(5) + (-5)(x) + (-5)(5) + 25
x^{3} + 5x^{2} - 5x -25 + 25
x^{3} + 5x^{2} - 5x

Question:3(ii) Simplify .

(a^2+5)(b^3+3)+5

Answer:

This can be simplified as

a^{2} + 5) X ( b^{3} + 3) + 5 = ( a^{2} )( b^{3} ) + ( a^{2} )(3) + (5)( b^{3} ) + (5)(3) + 5
a^{2}b^{3} + 3a^{2} + 5b^{3} + 15+5
a^{2}b^{3} + 3a^{2} + 5b^{3} + 20

Question:3(iii) Simplify.

(t+s^2)(t^2-s)

Answer:

simplifications can be

(t + s^{2} )( t^{2} - s) = (t)( t^{2} ) + (t)(-s) + ( s^{2} )( t^{2} ) + ( s^{2} )(-s)
t^{3} - ts + s^{2}t^{2} - s^{3}

Question:3(iv) Simplify.

(a+b)(c-d)+(a-b)(c+d)+2 (ac+bd)

Answer:

(a + b) X ( c -d) + (a - b) X (c + d) + 2(ac + bd )
= (a)(c) + (a)(-d) + (b)(c) + (b)(-d) + (a)(c) + (a)(d) + (-b)(c) + (-b)(d) + 2(ac + bd )
= ac - ad + bc - bd + ac +ad -bc - bd + 2(ac + bd )
= 2(ac - bd ) + 2(ac +bd )
= 2ac - 2bd + 2ac + 2bd
= 4ac

Question:3(v) Simplify.

(x+y)(2x+y)+(x+2y)(x-y)

Answer:

(x + y) X ( 2x + y) + (x + 2y) X (x - y)
=(x)(2x) + (x)(y) + (y)(2x) + (y)(y) + (x)(x) + (x)(-y) + (2y)(x) + (2y)(-y)
= 2 x^{2} + xy + 2xy + y^{2} + x^{2} - xy + 2xy - 2 y^{2}
=3 x^{2} + 4xy - y^{2}

Question:3(vi) Simplify.

(x+y)(x^2-xy+y^2)

Answer:

simplification is done as follows

(x + y) X ( x^{2} -xy + y^{2} ) = x X ( x^{2} -xy + y^{2} ) + y ( x^{2} -xy + y^{2} )
x^{3} -x^{2}y + xy^{2} + yx^{2} - xy^{2} + y^{3}
x^{3}+ y^{3}

Question:3(vii) Simplify.

(1.5x-4y)(1.5x+4y+3)-4.5x+12y

Answer:

(1.5x - 4y) X (1.5x + 4y + 3) - 4.5x + 12y = (1.5x) X (1.5x + 4y + 3) -4y X (1.5x + 4y + 3) - 4.5x + 12y
= 2.25 x^{2} + 6xy + 4.5x - 6xy - 16 y^{2} - 12y -4.5x + 12 y
= 2.25 x^{2} - 16 y^{2}

Question:3(viii) Simplify.

(a+b+c)(a+b-c)

Answer:

(a + b + c) X (a + b - c) = a X (a + b - c) + b X (a + b - c) + c X (a + b - c)
a^{2} + ab - ac + ab + b^{2} -bc + ac + bc - c^{2}
a^{2} + b^{2} - c^{2} + 2ab

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.11 standerd identities

Question:1(i) Put -b in place of b in identity 1. Do you get identity 2?

Answer:

Identity 1 \Rightarrow (a+b)^{2} = a^{2} + 2ab + b^{2}
If we replace b with -b in identity 1
We get,
a^{2} + 2a(-b) + (-b)^{2} = a^{2} - 2ab + b^{2}
which is equal to
(a-b)^{2} which is identity 2
So, we get identity 2 by replacing b with -b in identity 1

NCERT free solutions for class 8 maths chapter 9 algebraic expressions and identities topic 9.11 standard identities

Question:1 Verify Identity (IV), for a=2,b=3,x=5 .

Answer:

Identity IV
(a + x)(b + x) = x^{2} + (a+b)x + ab
So, it is given that a = 2, b = 3 and x = 5
Lets put these value in identity IV
(2 + 5)(3 + 5) = 5^{2} + (2 + 3)5 +2 X 3
7 X 8 = 25 + 5 X 5 + 6
56 = 25 + 25 + 6
= 56
L.H.S. = R.H.S.
So, by this we can say that identity IV satisfy with given value of a,b and x

Question:2 Consider, the special case of Identity (IV) with a = b, what do you get? Is it related to Identity

Answer:

Identity IV is \Rightarrow (a +x)(b+x) = x^{2} + (a+b)x + ab
If a =b than

(a + x)(a + x) = x^{2} + (a+a)x + a\times a
(a+x)^{2} = x^{2} + 2ax + a^{2}
Which is identity I

Question:3 Consider, the special case of Identity (IV) with a=-c and b=-c What do you get? Is it related to Identity ?

Answer:

Identity IV is \Rightarrow (a+x )(b +x) = x^{2} + (a+b)x + ab
If a = b = -c than,
(x - c)(x - c) = x^{2} + (-c + (-c))x + (-c) \times (-c)
(x-c)^{2} = x^{2} + -2cx + c^{2}
Which is identity II

Question:4 Consider the special case of Identity (IV) with b=-a . What do you get? Is it related to Identity?

Answer:

Identity IV is \Rightarrow (a+x )(b +x) = x^{2} + (a+b)x + ab
If b = -a than,

(x + a)(x - a) = x^{2} + (a +(-a))x + (-a) \times a
x^{2} - a^{2}
Which is identity III

NCERT solutions for class 8 maths chapter 9 algebraic expressions and identities-Exercise: 9.5

Question:1(i) Use a suitable identity to get each of the following products.

(x+3)(x+3)

Answer:

(x + 3) X (x +3) = (x +3)^{2}
So, we use identity I for this which is
(a+b)^{2} = a^{2} + 2ab + b^{2}
In this a=x and b = x
(x+3)^{2} = x^{2} + 2(x)(3)+ 3^{2}
x^{2} + 6x+ 9

Question:1(ii) Use a suitable identity to get each of the following products in bracket.

(2y+5)(2y+5)

Answer:

(2y + 5) X ( 2y + 5) = (2y +5)^{2}
We use identity I for this which is
(a+b)^{2} = a^{2} + 2ab + b^{2}
IN this a = 2y and b = 5
(2y+5)^{2} = (2y)^{2} + 2(2y)(5) + 5^{2}
(2y+5)^{2} = 4y^{2} + 20y + 25

Question:1(iii) Use a suitable identity to get each of the following products in bracket.

(2a-7)(2a-7)

Answer:

(2a -7) X (2a - 7) = (2a - 7)^{2}
We use identity II for this which is
(a-b)^{2} = a^{2} - 2ab + b^{2}
in this a = 2a and b = 7
(2a-7)^{2} = (2a)^{2} - 2(2a)(7) + 7^{2}
4a^{2} - 28a + 49

Question:1(iv) Use a suitable identity to get each of the following products in bracket.

(3a - \frac{1}{2}) (3a -\frac{1}{2} )

Answer:

(3a - \frac{1}{2}) \times (3a -\frac{1}{2} ) = ((3a - \frac{1}{2}))^{2}
We use identity II for this which is
(a-b)^{2} = a^{2} -2ab + b^{2}
in this a = 3a and b = -1/2
(3a-\frac{1}{2})^{2} = (3a)^{2} -2(3a)(\frac{1}{2}) + (\frac{1}{2})^{2}
9a^{2} -3a + \frac{1}{4}

Question:1(v) Use a suitable identity to get each of the following products in bracket.

(1.1m - 4)(1.1m+4)

Answer:

(1.1m - 4)(1.1m+4)
We use identity III for this which is
(a - b)(a + b) = a^{2} - b^{2}
In this a = 1.1m and b = 4
(1.1m - 4)(1.1m+4) = (1.1m)^{2} - (4)^{2}
= 1.21 m^{2} - 16

Question:1(vi) Use a suitable identity to get each of the following products in bracket.

(a^2+b^2)(-a^2+b^2)

Answer:

take the (-)ve sign common so our question becomes
-(a^{2}+b^{2})(a^{2}-b^{2})
We use identity III for this which is
(a - b)(a + b) = a^{2} - b^{2}
In this a = a^{2} and b = b^{2}

-(a^{2}+b^{2})(a^{2}-b^{2}) = -((a^{2})^{2} -(b^{2})^{2}) = -a^{4} + b^{4}

Question:1(vii) Use a suitable identity to get each of the following.

(6x-7) (6x+7)

Answer:

(6x -7) X (6x - 7) = (6x-7)^{2}
We use identity III for this which is
(a - b)(a + b) = a^{2} - b^{2}
In this a = 6x and b = 7
(6x -7) X (6x - 7) = (6x)^{2} - (7)^{2} = 36x^{2} - 49

Question:1(viii) Use a suitable identity to get each of the following product.

(-a+c)(-a+c)

Answer:

take (-)ve sign common from both the brackets So, our question become
(a -c) X (a -c) = (a -c)^{2}
We use identity II for this which is
(a-b)^{2} =a^{2} -2ab + b^{2}
In this a = a and b = c
(a-c)^{2} =a^{2} -2ac + c^{2}

Question:1(ix) Use a suitable identity to get each of the following product.

(\frac{x}{2}+ \frac{3y}{4})(\frac{x}{2}+ \frac{3y}{4})

Answer:

(\frac{x}{2}+ \frac{3y}{4}) \times (\frac{x}{2}+ \frac{3y}{4}) = (\frac{x}{2}+ \frac{3y}{4})^{2}

We use identity I for this which is
(a+b)^{2} =a^{2}+2ab + b^{2}
In this a = \frac{x}{2} and b = \frac{3y}{4}


\frac{x^{2}}{4} + \frac{3xy}{4} + \frac{9y^{2}}{16}

Question:1(x) Use a suitable identity to get each of the following products.

(7a-9b)(7a-9b)

Answer:

(7a-9b) \times (7a-9b) = (7a-9b)^{2}


We use identity II for this which is
(a-b)^{2} =a^{2}-2ab + b^{2}
In this a = 7a and b = 9b
(7a-9b)^{2} =(7a)^{2}-2(7a)(9b) + (9b)^{2}
49a^{2}-126ab + 81b^{2}

Question:2(i) Use the identity (x+a) (x+b) = x^2+(a+b)x+ab to find the following products.

(x+3)(x+7)

Answer:

We use identity (x+a) (x+b) = x^2+(a+b)x+ab
in this a = 3 and b = 7
(x+3)(x+7) = x^2+(3+7)x+3 \times 7
x^2+10x+ 21

Question:2(ii) Use the identity (x+a)(x+b)=x^2+(a+b)x+ab to find the following products.

(4x+5)(4x+1)

Answer:

We use identity (x+a)(x+b)=x^2+(a+b)x+ab
In this a= 5 , b = 1 and x = 4x
(4x+5)(4x+1) = (4x)^2+(5+1)4x+(5)(1)
16x^2+24x+5

Question:2(iii) Use the identity (x+a)(x+b)= x^2+(a+b)x+ab to find the following products.

(4x-5)(4x-1)

Answer:

We use identity (x+a)(x+b)= x^2+(a+b)x+ab
in this x = 4x , a = -5 and b = -1
(4x-5)(4x-1) = (4x)^2+(-5-1)4x+(-5)(-1)
16x^2 - 24x+ 5

Question:1(iv) Use the identity (x+a)(x+b)=x^2+(a+b)x+ab to find the following products.

(4x+5)(4x-1)

Answer:

We use identity (x+a)(x+b)=x^2+(a+b)x+ab
In this a = 5 , b = -1 and x = 4x
(4x+5)(4x-1) = (4x)^2+(5+(-1))4x+(5)(-1)
16x^2+16x- 5

Question:2(v) Use the identity (x+a)(x+b)=x^2+(a+b)x+ab to find the following products.

(2x+5y)(2x+3y)

Answer:

We use identity (x+a)(x+b)=x^2+(a+b)x+ab
In this a = 5y , b = 3y and x = 2x
(2x+5y)(2x+3y) = (2x)^2+(5y+3y)(2x)+(5y)(3y)
4x^2+16xy + 15y^{2}

Question:2(vi) Use the identity (x+a)(x+b)=x^2+(a+b)x+ab to find the following products.

(2a^2+9)(2a^2+5)

Answer:

We use identity (x+a)(x+b)=x^2+(a+b)x+ab
In this a = 9 , b = 5 and x = <img alt="2a^{2}" height="16"

src="https://lh5.googleusercontent.com/2qHQF6RatvqmP_IzaprdObn1TW7Qc6P5ahuw5OBgw979_B5ENMeSRnBhk9M65bsGhcIIOjA5Z-Tfx4RDq34UjzRxIxPbAH48O8Ack3-cw0InSk7MCot84kU1ew5darMTXngAh6s" style="margin-left: 0px; margin-top: 0px;" width="24" />
(2a^{2}+9)(2a^{2}+5) = (2a^{2})^2+(9+5)2a^{2}+(9)(5)
4a^{4} + 28a^{2} + 45

Question:2(vii) Use the identity (x+a) (x+b)=x^2+(a+b)x+ab to find the following products.

(xyz-4) (xyz-2)

Answer:

We use identity (x+a)(x+b)=x^2+(a+b)x+ab
In this a = -4 , b = -2 and x = xyz
(xyz-4)(xyz-2) = (xyz)^2+((-4)+(-2))xyz+(-4)(-2)
x^{2}y^{2}z^{2} -6xyz + 8

Question:3(i) Find the following squares by using the identities.

(b-7)^2

Answer:

We use identity
(a-b)^{2} = a^{2} - 2ab + b^{2}
In this a =b and b = 7
(b-7)^{2} = b^{2} - 2(b)(7) + 7^{2}
b^{2} - 14b + 49

Question:3(ii) Find the following squares by using the identities.

(xy+3z)^2

Answer:

We use
(a+b)^{2} = a^{2} + 2ab + b^{2}

In this a = xy and b = 3z
(xy+3z)^{2} = (xy)^{2} + 2(xy)(3z) + (3z)^{2}
x^{2}y^{2} + 6xyz+ 9z^{2}

Question:3(iii) Find the following squares by using the identities.

(6x^2-5y)^2

Answer:

We use
(a-b)^{2} = a^{2} - 2ab + b^{2}
In this a = 6x^{2} and b = 5y^{2}
(6x-5y)^{2} = (6x)^{2} - 2(6x)(5y) + (5y)^{2}
36x^{2} - 60xy + 25y^{2}

Question:3(iv) Find the following squares by using the identities.

(\frac{2}{3}m+\frac{3}{2}n)^2

Answer:

we use the identity
(a+b)^{2} = a^{2} + 2ab + b^{2}
In this a = \frac{2m}{3} and b = \frac{3n}{2}


\frac{4m^{2}}{9} + 2mn + \frac{9n^{2}}{4}

Question:3(v) Find the following squares by using the identities.

(0.4p-0.5q)^2

Answer:

we use
(a-b)^{2} = a^{2} - 2ab + b^{2}
In this a = 0.4p and b =0.5q
(0.4p-0.5q)^{2} = (0.4p)^{2} - 2(0.4p)(0.5q) + (0.5q)^{2}
0.16p^{2} - 0.4pq + 0.25q^{2}

Question:3(vi) Find the following squares by using the identities.

(2xy+5y)^2

Answer:

we use the identity
(a+b)^{2} = a^{2} + 2ab + b^{2}
In this a = 2xy and b =5y
(2xy+5y)^{2} = (2xy)^{2} + 2(2xy)(5y) + (5y)^{2}
4x^{2}y^{2} + 20xy^{2} + 25y^{2}

Question:4(i) Simplify:

(a^2-b^2)^2

Answer:

we use
(a-b)^{2} = a^{2} - 2ab + b^{2}
In this a = a^{2} and b = b^{2}
(a^{2}-b^{2})^{2} = (a^{2})^{2} - 2(a^{2})(b^{2}) + (b^{2})^{2}
a^{4} - 2a^{2}b^{2} + b^{4}

Question:4(ii) Simplify.

(2x+5)^2-(2x-5)^2

Answer:

we use
a^{2} - b^{2} = (a-b)(a+b)
In this a = (2x + 5) and b = (2x - 5)
(2x + 5)^{2} - (2x - 5)^{2} = ( (2x + 5)- (2x - 5))( (2x + 5)+ (2x - 5))
( 2x + 5- 2x + 5)( 2x + 5+ 2x - 5)
= (4x)(10)
=40x

or

remember that

(a+b)^2-(a-b)^2=4ab

here a= 2x, b= 5

4ab=4\times 2x \times 5=40x

Question:4(iii) Simplify.

(7m-8n)^2+(7m+8n)^2

Answer:

we use
(a-b)^{2} = a^{2} -2ab + b^{2} and (a+b)^{2} = a^{2} +2ab + b^{2}
In this a = 7m and b = 8n
(7m-8n)^{2} = (7m)^{2} -2(7m)(8n) + (8n)^{2}
49m^{2} -112mn + 64n^{2}
and
(7m+8n)^{2} = (7m)^{2} +2(7m)(8n) + (8n)^{2}
49m^{2} +112mn + 64n^{2}

So, (7m - 8n)^{2} + (7m + 8n)^{2} = 49m^{2} -112mn + 64n^{2} + 49m^{2} +112mn + 64n^{2}
2(49m^{2} + 64n^{2})

or

remember that

(a-b)^2+(a+b)^2=2(a^2+b^2)

Question: 4(iv) Simplify.

(4m+5n)^2+(5m+4n)^2

Answer:

we use
(a+b)^{2} = a^{2} +2ab + b^{2}
1 ) In this a = 4m and b = 5n

(4m+5n)^{2} = (4m)^{2} +2(4m)(5n) + (5n)^{2}
16m^{2} +40mn + 25n^{2}
2 ) in this a = 5m and b = 4n
(5m+4n)^{2} = (5m)^{2} +2(5m)(4n) + (4n)^{2}
25m^{2} +40mn + 16n^{2}

So, (4m + 5n)^{2} + (5m + 4n)^{2} = 16m^{2} +40mn + 25n^{2} + 25m^{2} +40mn + 16n^{2}
41m^{2} +80mn + 41n^{2}

Question: 4(v) Simplify.

(2.5p-1.5q)^2-(1.5p-2.5q)^2

Answer:

we use
a^{2}- b^{2} = (a-b)(a+b)
1 ) In this a = (2.5p- 1.5q) and b = (1.5p - 2.5q)
(2.5p- 1.5q)^{2}- (1.5p- 2.5q)^{2} = ( (2.5p- 1.5q)- (1.5p- 2.5q))( (2.5p- 1.5q)+ (1.5p- 2.5q))
( 2.5p- 1.5q- 1.5p + 2.5q)(2.5p- 1.5q+ 1.5p- 2.5q)
= 4(p + q ) (p - q)
= 4 (p^{2} - q^{2})

Question:4(vi) Simplify.

(ab+bc)^2-2ab^2c

Answer:

We use identity
(a+b)^{2} = a^{2} + 2ab + b^{2}
In this a = ab and b = bc
(ab+bc)^{2} = (ab)^{2} + 2(ab)(bc) + (bc)^{2}
a^{2}b^{2} + 2ab^{2}c + b^{2}c^{2}
Now, a^{2}b^{2} + 2ab^{2}c + b^{2}c^{2} - 2ab^{2}c
a^{2}b^{2} + b^{2}c^{2}

Question:4(vii) Simplify.

(m^2 -n^2m)^2+2m^3n^2

Answer:

We use identity
(a-b)^{2} = a^{2} - 2ab + b^{2}
In this a = m^{2} and b = n^{2}m
(m^{2}-n^{2}m)^{2} = (m^{2})^{2} - 2(m^{2})(n^{2}m) + (n^{2}m)^{2}
m^{4} - 2m^{3}n^{2} + n^{4}m^{2}
Now, m^{4} - 2m^{3}n^{2} + n^{4}m^{2} + 2m^{3}n^{2}
m^{4} + n^{4}m^{2}

Question:5(i) Show that

(3x+7)^2-84x=(3x-7)^2

Answer:

L.H.S. = (3x+7)^2 - 84x = 9x^2 + 42x + 49 - 84x

= 9x^2 - 42 x +49

= (3x - 7)^2

= R.H.S.

Hence it is prooved

Question:5(ii) Show that

(9p-5q)^2+180pq=(9p+5q)^2

Answer:

L.H.S. = (9p-5q)^2+180pq = 81p^2 - 90pq + 25q^2 + 180pq (Using (a-b)^2 = a^2 - 2ab + b^2 )

= 81p^2 +90pq + 25q^2

= (9p + 5q)^2\left ( (a+b)^2 = a^2 + 2ab + b^2 \right )

= R.H.S.

Question:5(iii) Show that.

(\frac{4}{3}m-\frac{3}{4}n)^2 +2mn=\frac{16}{9}m^2+\frac{9}{16}n^2

Answer:

First we will solve the LHS :

= (\frac{4}{3}m-\frac{3}{4}n)^2 +2mn = \frac{16}{9}m^2 - 2mn + \frac{9}{16}n^2 + 2mn

or = \frac{16}{9}m^2 + \frac{9}{16}n^2

= RHS

Question:5(iv) Show that.

(4pq+3q)^2-(4pq-3q)^2=48pq^2

Answer:

Opening both brackets we get,

(4pq+3q)^2-(4pq-3q)^2 = 16p^2q^2 + 24pq^2 + 9q^2 - (16p^2q^2 - 24pq^2 + 9q^2)

= 16p^2q^2 + 24pq^2 + 9q^2 - 16p^2q^2 + 24pq^2 - 9q^2)

= 48pq^2

= R.H.S.

Question:5(v) Show that

(a-b)(a+b) + (b-c) ( b +c)+(c-a)(c+a)=0

Answer:

Opening all brackets from the LHS, we get :

(a-b)(a+b) + (b-c) ( b +c)+(c-a)(c+a)\\\\ =\ a^2 +ab - ab- b^2 + b^2+bc - bc -c^2 + c^2 +ca - ac -a^2

= 0 = RHS

Question:6(i) Using identities, evaluate.

71^2

Answer:

We will use the identity:

(a + b)^2 = a^2 + 2ab + b^2

So, 71^2 = (70 +1)^2 = 70^2 + 2(70)(1) + 1^2

= 4900 + 140 + 1

= 5041

Question:6(ii) Using identities, evaluate.

99^2

Answer:

Here we will use the identity :

(a - b)^2 = a^2 - 2ab + b^2

So : 99^2 = (100 - 1) ^2 = 100^2 - 2(100)(1) + 1^2

or = 10000 - 200 + 1

= 9801

Question:6(iii) Using identities, evaluate.

102^2

Answer:

Here we will use the identity :

(a+b)^2 = a^2 +2ab + b^2

So :

102^2 = (100 + 2)^2 = 100^2 + 2(100)(2) + 2^2

or = 10000 + 400 + 4

= 10404

Question:6(iv) Using identities, evaluate.

998^2

Answer:

Here we will the identity :

998^2=(1000 - 2)^2 = 1000^2 - 2(1000)(2) + 2^2

or = 1000000 - 4000+ 4

or = 996004

Question:6(v) Using identities, evaluate.

5.2^2

Answer:

Here we will use :

(a + b)^2 = a^2 + 2ab + b^2

Thus

(5.2)^2 = (5.0 + 0.2)^2 = 5^2 + 2(5)(0.2) + (0.2)^2

or = 25 + 2 + 0.04

= 27.04

Question:6(vi) Using identities, evaluate.

297 \times 303

Answer:

This can be written as :

297\times303 = (300-3)\times(300+3)

using (a-b)(a+b)=a^2-b^2

or = 90000 - 9

= 89991

Question:6(vii) Using identities, evaluate.

78 \times 82

Answer:

This can be written in form of :

78\times82 = (80 - 2) \times(80+2)

or = 80^2 - 2^2\because \left ( a-b \right )\left ( a+b \right ) = a^2 - b^2

or = 6400- 4 = 6396

Question:6(viii) Using identities, evaluate.

8.9^2

Answer:

Here we will use the identity :

(a - b)^2 = a^2 - 2ab + b^2

Thus :

8.9^2 = (9 - 0.1) ^2 = 9^2 - 2(9)(0.1) + 0.1^2

or = 81 - 1.8 + 0.01

or = 79.21

Question:6(ix) Using identities, evaluate.

10.5\times9.5

Answer:

This can be written as :

10.5\times9.5 = (10 +0.5)\times(10-0.5)

or = 10^2 - 0.5^2\because (a+b)(a-b) = a^2 - b^2

or = 100 - 0.25

or = 99.75

Question:7(i) Using a^2-b^2=(a+b)(a-b) , find

51^2-49^2

Answer:

We know,

a^2-b^2=(a+b)(a-b)

Using this formula,

51^2-49^2 = (51 + 49)(51 - 49)

= (100)(2)

= 200

Question:7(ii) Using a^2-b^2=(a+b)(a-b) , find

(1.02)^2-(0.98)^2

Answer:

We know,

a^2-b^2=(a+b)(a-b)

Using this formula,

(1.02)^2-(0.98)^2 = (1.02 + 0.98)(1.02 - 0.98)
= (2.00)(0.04)

= 0.08

Question:7(iii) Using a^2-b^2=(a+b)(a-b) , find.

153^2-147^2

Answer:

We know,

a^2-b^2=(a+b)(a-b)

Using this formula,

153^2-147^2 = (153 - 147)(153 +147)

=(6) (300)

= 1800

Question:7(iv) Using a^2-b^2=(a+b )(a-b) , find

12.1^2-7.9^2

Answer:

We know,

a^2-b^2=(a+b)(a-b)

Using this formula,

(1.02)^2-(0.98)^2 = (1.02 + 0.98)(1.02 - 0.98)

= (2.00)(0.04)

= 0.08

Question:8(i) Using (x+a)(x+b)=x^2+(a+b)x+ab103 \times 104

Answer:

We know,

(x+a)(x+b)=x^2+(a+b)x+ab

Using this formula,

103 \times 104 = (100 + 3)(100 + 4)

Here x =100, a = 3, b = 4

\therefore103 \times 104= 100^2+(3+4)100+(3\times4)

= 10000+1200+12

= 11212

Question:8(ii) Using (x+a)(x+b)=x^2+(a+b)x+ab , find

5.1\times 5.2

Answer:

We know,

(x+a)(x+b)=x^2+(a+b)x+ab

Using this formula,

5.1\times 5.2 = (5 + 0.1)(5 + 0.2)

Here x =5, a = 0.1, b = 0.2

\therefore5.1\times 5.2=5^2+(0.1 + 0.2)5+(0.1\times0.2)

= 25+1.5+0.02

= 26.52

Question:8(iii) Using (x+a)(x+b)=x^2+(a+b)x+ab , find

103 \times 98

Answer:

We know,

(x+a)(x+b)=x^2+(a+b)x+ab

Using this formula,

103 \times 98 = (100 + 3)(100 - 2) = (100 + 3){100 + (-2)}

Here x =100, a = 3, b = -2

\therefore103 \times 98= 100^2+(3 + (-2))100+(3\times(-2))

= 10000+100-6

= 10094

Question: 8(iv) Using (x+a)(x+b)=x^2+(a+b)x+ab , find

9.7 \times 9.8

Answer:

We know,

(x+a)(x+b)=x^2+(a+b)x+ab

Using this formula,

9.7 \times 9.8 = (10 - 0.3)(10 - 0.2) = {10 + (-0.3)}{10 + (-0.2)}

Here x =10, a = -0.3, b = -0.2

\therefore9.7 \times 9.8= 10^2+((-0.3) + (-0.2))10+((-0.3)\times(-0.2))

= 100-5+0.06

= 95.

NCERT Class 8 Mathematics Solutions

Chapter 01 - Rational Numbers

Chapter 02 - Linear Equations in One Variable

Chapter 03 -Understanding Quadrilaterals

Chapter 04 - Practical Geometry

Chapter 05 - Data Handling

Chapter 06 - Squares and Square Roots

Chapter 07 - Cubes and Cube Roots

Chapter 08 - Comparing Quantities

Chapter 09 - Algebraic Expressions and Identities

Chapter 10 - Visualising Solid Shapes

Chapter 11 - Mensuration

Chapter 12 - Exponents and Powers

Chapter 13 - Direct and Indirect proportions

Chapter 14 - Factorisation

Chapter 15 - Introduction to Graphs

Chapter 16 - Playing with Numbers

Want to know more

Please fill in the details below:

INNER POST ADS

Latest IITJEE Articles$type=three$c=3$author=hide$comment=hide$rm=hide$date=hide$snippet=hide

Latest NEET Articles$type=three$c=3$author=hide$comment=hide$rm=hide$date=hide$snippet=hide

Name

Admissions,1,Alternating Current,60,AP EAMCET 2020,1,Basic Maths,2,BCECE 2020,1,best books for iit jee,2,best coaching institute for iit,1,best coaching institute for iit jee preparation,1,best iit jee coaching delhi,1,best iit jee coaching in delhi,2,best study material for iit jee,4,BITSAT Registration 2020,1,Blog,62,books for jee preparation,1,books recommended by iit toppers,3,Capacitance,3,CBSE,1,CBSE accounts exam,1,CBSE boards,1,CBSE NEET,9,cbse neet 2019,3,CBSE NEET 2020,1,cbse neet nic,1,Centre of Mass,2,Chemistry,58,Class 12 Physics,15,coaching for jee advanced,1,coaching institute for iit jee,2,Collision,2,COMEDK UGET 2020 Application Form,1,COMEDK UGET 2020 Exam Form,1,COMEDK UGET news,1,CUCET 2020,2,Current Electricity,4,CVR college,1,Digestion and Absorption Notes PDF,1,Electromagnetic Induction,3,Electronics,1,Electrostatics,3,Energy,1,Engineering & Medical,1,Fluid Mechanics,4,Gravitation,2,GUJCET 2020 Application Form,1,Heat,4,iit admission,1,iit advanced,1,iit coaching centre,3,iit coaching centre in delhi,2,iit coaching classes,2,iit coaching in delhi,1,iit coaching institute in delhi,1,iit entrance exam,1,iit entrance exam syllabus,2,iit exam pattern,2,iit jee,5,iit jee 2019,3,iit jee advanced,2,iit jee books,3,iit jee coaching,2,iit jee exam,3,iit jee exam 2019,1,iit jee exam pattern,3,iit jee institute,1,iit jee main 2019,2,iit jee mains,3,iit jee mains syllabus,2,iit jee material,1,iit jee online test,3,iit jee practice test,3,iit jee preparation,6,iit jee preparation in delhi,2,iit jee preparation time,1,iit jee preparation tips by toppers,2,iit jee question paper,1,iit jee study material,3,iit jee study materials,2,iit jee syllabus,2,iit jee syllabus 2019,2,iit jee test,3,iit preparation,2,iit preparation books,5,iit preparation time table,2,iit preparation tips,2,iit syllabus,2,iit test series,3,IITJEE,100,Important Biology Notes for NEET Preparation,1,IPU CET,1,JEE Advanced,83,jee advanced exam,2,jee advanced exam pattern,1,jee advanced paper,1,JEE Books,1,JEE Coaching Delhi,3,jee exam,3,jee exam 2019,6,JEE Exam Pattern,2,jee exam pattern 2019,1,jee exam preparation,1,JEE Main,85,jee main 2019,4,JEE Main 2020,1,JEE Main 2020 Application Form,2,JEE Main 2020 news,2,JEE Main 2020 Official Answer Key,1,JEE Main 2020 Registration,1,JEE Main 2020 Score,1,JEE Main application form,1,jee main coaching,1,JEE Main eligibility criteria,3,jee main exam,1,jee main exam 2019,3,jee main online question paper,1,jee main online test,3,JEE Main Paper-2 Result,1,jee main registration,2,jee main syllabus,2,JEE mains 2020,1,jee mains question bank,1,jee mains test papers,3,JEE Mock Test,2,jee notes,1,jee past papers,1,JEE Preparation,2,jee preparation in delhi,1,jee preparation material,4,JEE Study Material,1,jee syllabus,6,JEE Syllabus Chemistry,1,JEE Syllabus Maths,1,JEE Syllabus Physics,1,jee test series,3,KCET - 2020,1,Kinematics,1,Latest article,5,Latest Articles,61,Latest News,34,latest news about neet exam,1,Laws of Motion,2,Magnetic Effect of Current,3,Magnetism,3,MHT CET 2020,2,MHT CET 2020 exam schedule,1,Modern Physics,1,NCERT Solutions,15,neet,3,neet 2019,1,neet 2019 eligibility criteria,1,neet 2019 exam date,2,neet 2019 test series,2,NEET 2020,2,NEET 2020 Application Form,1,NEET 2020 Eligibility Criteria,1,NEET 2020 Registration,1,neet application form,1,neet application form 2019 last date,1,Neet Biology Syllabus,1,Neet Books,3,neet eligibility criteria,3,neet exam 2019,7,neet exam application,1,neet exam date,1,neet exam details,1,neet exam pattern,6,neet exam pattern 2019,2,neet examination,1,neet mock test 2019,1,Neet Notes,3,Neet Online Application Form,3,neet online test,2,neet past papers,1,neet physics syllabus,1,neet practice test,2,NEET preparation books,1,neet qualification marks,1,NEET question paper 2019,1,neet question papers,1,neet registration,1,Neet Study Material,3,neet syllabus,6,neet syllabus 2019,5,NEET Syllabus 2020,1,neet syllabus chemistry,1,neet syllabus for biology,1,neet syllabus for physics,1,neet test series,1,neet ug 2019,2,news,5,online study material for iit jee,1,Optical Instruments,1,Physics,110,physics books for iit jee,1,Power,1,Practical Physics,1,Quiz,5,Ray Optics,1,Rotational Motion,3,SHM,3,Simple Harmonic Motion,3,study materials for iit jee,1,Study Notes,110,study notes for iit jee,1,Thermodynamics,4,TS EAMCET Notification,2,Units and Dimensions,1,UPSEE 2020,1,UPSEE 2020 Application Form,2,UPSEE EXAM,1,Vectors,2,VITEE Application form,1,Wave Motion,3,Wave Optics,1,WBJEE 2020 Admit Card,1,WBJEE 2020 Answer Key,1,Work,1,
ltr
static_page
BEST NEET COACHING CENTER | BEST IIT JEE COACHING INSTITUTE | BEST NEET & IIT JEE COACHING: ncert-solutions-class-8-maths-ch-9-algebraic-expressions-and-identities
ncert-solutions-class-8-maths-ch-9-algebraic-expressions-and-identities
BEST NEET COACHING CENTER | BEST IIT JEE COACHING INSTITUTE | BEST NEET & IIT JEE COACHING
https://www.cleariitmedical.com/p/ncert-solutions-class-8-maths-ch-9.html
https://www.cleariitmedical.com/
https://www.cleariitmedical.com/
https://www.cleariitmedical.com/p/ncert-solutions-class-8-maths-ch-9.html
true
7783647550433378923
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS CONTENT IS PREMIUM Please share to unlock Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy

STAY CONNECTED