ML Aggarwal Solution Class 9 Chapter 3 Expansions Exercise 3.1

 Exercise 3.1

Question 1

(i) (2x+7y)2

It is in the form of (a+b)2=a2+2ab+b2

∴a=2x, b=7y

∴(2x+7y)2=(2x)2+2.2x.7y+(7y)2

=4x2+28xy+49y2


(ii) (12x+23y)2

Sol :

(12x)2+2×12×x×23×y+(23y)2

x24+2xy3+49y2


Question 2

(i) (3x+12x)2

It is in the form of (a+b)2=a2+2ab+b2

(3x)2+2.3x.12x+(12x)2

9x3+3+14x2


(ii) (3x2y+5z)2

It is in the form of (a+b)2=a2+2ab+b2

Here a=3x2y , b=5x

(3x2y)2+2.3x2y.5z+(5z)2

9x4y2+30x2yz+25z2


Question 3

(i) (3x12x)2

It is in the form of (ab)2=a22ab+b2

Here, a=3x ; b=12x

(3x)22.3x.12x+(12x)2

32x23+122x2

9x23+14x2


(ii) (12x32y)2

It is in the form of (ab)2=a22ab+b2

Here, a=12x ; b=32y

(12x)22×1x2×32y+(32y)2

x243xy2+9y24


Question 4

(i) (x+3)(x+5)

⇒x(x+5)+3(x+5)

x2+5x+3x+15

x2+8x+15


(ii) (x+3)(x-5)

⇒x(x-5)+3(x-5)

⇒x.x-x.5+3.x-3.5

⇒x2-5x+3x-15

⇒x2-2x-15


(iii) (x-7)(x+9)

⇒x(x+9)-7(x+9)

⇒x.x+9.x-7.x-7.9

⇒x2+9x-7x-63

⇒x2+2x-63


(iv) (x-2y)(x-3y)

⇒x(x-3y)-2y(x-3y)

⇒x.x-x.3y-2y.x+2y.3y

⇒x2-3xy-2xy+6y2

⇒x2-5xy+6y2


Question 5

(i) (x-2y-z)2

It is in the form of (a+b+c)2=a2+b2+c2+2(ab+bc+ca)

Here, a=x, b=-2y, c=-z

⇒x2+(-2y)2+(-z)2+2(x(-2y)+(-2y)(-z)+(-z)x)

⇒x2+4y2+z2+2(-2xy+2yz-zx)

⇒x2+4y2+z2+4yz-4xy-2zx


(ii) (2x-3y+4z)2

It is in the form of (a+b+c)2=a2+b2+c2+2(ab+bc+ca)

Here a=2x, b=-3y, c=4z

⇒(2x)2+(-3y)+(4z)+2(2x.(-3y)+(-3y)(4z)+(4z)(2x))

⇒4x2+4y2+16z2+2(-6xy-12yz+8xz)

⇒4x2+4y2+16z2-12xy-24yz+16xz


Question 6

(i) (2x+3x1)2

It is in the form of (a+b+c)2=a2+b2+c2+2(ab+bc+ca)

Here, a=2x , b=3x , c=-1

(2x)2+(3x)2+(1)2+2(2x.3x+3x(1)+(1)2x)

4x2+9x2+1+2(63x2x)

4x2+9x2+1+126x4x

4x2+9x26x4x+13


(ii) (23x32x1)2

Sol :

It is in the form of (a+b+c)2=a2+b2+c2+2(ab+bc+ca)

Here, a=23x,b=32x, c=-1

(23x)2+(32x)2+(1)2+2[23x(32x)+(32x)(1)+(1)(23x)]

49x294x2+1+2[1+32x23x]

49x294x2+1+2+62x4x3

49x294x2+3x4x31


Question 7

(i) (x+2)3

Sol :

It is in the form of (a+b+c)2=a2+b2+c2+2(ab+bc+ca)

Here , a=x, b=2

∴⇒x3+3.x2.2+3.x.2+23

⇒x3+6.x2+3x.4+8

⇒x3+6x2+12x+8


(ii) (20+b)3

Sol :

⇒(2a)3+3.(2a)2.b+3.2a.b2+b3

⇒8a3+3.4a2.b+6ab2+b3

⇒8a+12a2b+6ab2+b3


Question 8

(i) (3x+1x)3

Sol :

It is in the form of (a+b+c)3=a3+3a2b+3ab2+b3

a=3x ; b=1x

(3x)3+3.(3x)2.1x+3.3x.(1x)2+(1x)3

27x3+3.9x21x+9.x.1x2+1x3

27x3+27x+9x+1x3


(ii) (2x-1)3

Sol :

It is in the form of (a-b)3=a3-3a2b+3ab2-b3

Here, a=2x, b=1

∴(2x)3-3(2x)2.1+3(2x)(1)2-(1)3

⇒8x3-3.4x2+6x-1

⇒8x3-12x2+6x-1


Question 9

(i) (5x-3y)3

Sol :

It is in the form of (a-b)3=a3-3a2b+3ab2-b3

a=5x ; b=3y

∴ (5x)3-3.(5x)2.3y+3.5x.(3y)2-(3y)3

⇒125x3-3.25x2.3y+3.5x.9y2-27y3

⇒125x3-225x2y+135y2.x-27y3


(ii) (2x13y)3

Sol :

(2x)33.(2x)2.13y+3.2x.(13y)2(13y)3

8x33.4x2.13y+3.2x.19y2127y3

8x34x2y+2x3y2127y3


Question 10

(i) (a+b)2+(a-b)2

⇒a2+2ab+b2+a2-2ab+b2

⇒2a2+2b2

⇒2(a2+b2)


(ii) (a+b)2-(a-b)2

⇒(a2+2ab+b2)-(a2-2ab+b2)

⇒a2+2ab+b2-a2+2ab-b2

⇒2ab+2ab

⇒4ab


Question 11

(i) (a+1a)2+(a1a)2

(a2+2.a.1a+)+(a2+2.a.1a+1a2)

a2+2+1a2+a22+1a2

2a2+2a2

2(a2+1a2)


(ii) (a+1a)2(a1a)2

(a2+2.a.1a+1a2)(a22.a.1a+1a2)

a2+2+1a2a2+21a2

⇒2+2

⇒4


Question 12

(i) (3x-1)2-(3x-2)(3x+1)

⇒(3x)2-2.3x.1+12-3x(3x+1)+2(3x+1)

⇒9x2-6x+1-9x2-3x+6x+2

⇒3x+3

⇒3(x+1)


(ii) (4x+3y)2-(4x-3y)2-48

⇒(4x)2+2.3y.4x+(3y)2-((4x)2-2.4x.3y+(3y)2)-48

⇒16x2+24xy+9y2-16x2+24xy-9y2-48

⇒48xy-48

⇒48(xy-1)


Question 13

(i) (7p+9q)(7p-9q)

⇒7p(7p-9q)+9q(7p-9q)

⇒49p2-63pq+63pq-81q2

⇒49p2-81q2


(ii) (2x3x)(2x+3x)

(2x)2(3x)2

(2x)2(3x)2

⇒Since it is in the form of (a+b)(a-b)=a2-b2

4x29x2


Question 14

(i) (2x-y+3)(2x-y-3)

⇒((2x-y)+3)((2x-y)-3)

It is in the form of (a+b)(-a-b)=a2-b2

∴(2x-y)2-32
⇒(2x)2-2.2x.y+y2-9
⇒4x2-4xy+y2-9

(ii) (3x+y-5)(3x-y-5)
⇒(3x+(y-5))(3x-(y+5))
⇒[(3x-5)+y][(3x-5)-y]
⇒It is in the form of (a+b)(a-b)=a2-b2
∵a=3x-5 ; b=y
∴(3x-5)2-y2
⇒(3x)2-2.3x.5+52-y2
⇒9x2-30x+25-y2

Question 15

(i) (x+2x3)(x2x3)
((x3)+2x)((x3)2x)
It is in the form of (a+b)(a-b)=a2-b2
∵a=x-3 ; b=2x
(x3)2(2x)2
x22.x.3+324x2
x26x+94x2

(ii) (5-2x)(5+2x)(25+4x2)
It is in the form of (a+b)(a-b)=a2-b2
∴(52-(2x)2)(25+4x2)
⇒(25-4x2)(25+4x2)
⇒(25)2-(4x2)2
⇒625-16x4


Question 16

(i) (x+2y+3)(2y+x+7)
⇒x(2y+x+7)+2y(2x+x+7)+3(2y+x+7)
⇒2xy+x2+7x+4y2+2xy+14y+6y+3x+21
⇒x2+4y2+4xy+10x+20y+21

(ii) (2x+y+5)(2x+y-9)
⇒2x(2x+y-9)+y(2x+y-9)+5(2x+y-9)
⇒4x2+2xy-18x+2xy+y2-9y+10x+5y-45
⇒4x2+y2+4xy-8x-4y-45

(iii) (x-2y-5)(x-2y+3)
⇒x(x-2y+3)-2y(x-2y+3)-5(x-2y+3)
⇒x2-2xy+3x-2xy+4y2-6y-5x+10y-15
⇒x2+4y2-4xy-2x-4y-15

(iv) (3x-4y-2)(3x-4y-6)
⇒3x(3x-4y-6)-4y(3x-4y-6)-2(3x-4y-6)
⇒9x2-12xy-18x-12xy+16y2+24y-6x+8y+12
⇒9x2+16y2-24xy-24x+32y+12


Question 17

(i) (2p+3q)(4p2-6pq+9q2)
Sol :
(2p+3q)((2p)2-2p.3q+(3q)2)
It is in the form of (a+b)(a2-ab)b2) is
a3+b3
∴Here, a=2p ; b=3q
∴(2p)3+(3q)3
⇒8p3+27q3

(ii) (x+1x)(x21+1x2)
Sol :
It is in the form of (a+b)(a2-ab+b2) is a3+b3
∴Here a=x ; b=1x
x3+1x3

Question 18

(i) (3p-4q)(4p2+12pq+16q2)
(3p-4q)((3p)2+3p.4q+(4q)2)
It is in the form of (a-b)(a2+ab+b2) is a3-b3
∴Here 3p=a ; b=4q
∴(3p)3-(4q)3
⇒27p3-64q3

(ii) (x3x)(x2+3+9x2)
(x3x)(x2+x.3x+(32)2)
It is in the form of (a-b)(a2+ab+b2) is a3-b3
∴Here, a=x ; b=3x
x327x3

Question 19

Sol :
Given (2x+3y+4z)(4x2+9y2+16z2-6xy-12yz-8zx)
⇒(2x+3y+4z)((2x)2+(3y)2+(4z)2-2x.3y-3y.4z-4z.2x)
∴It is in the form of (a+b+c)(a2+b2+c2-ab-bc-ca)=a3+b3+c3-3abc
∴Here a=2x , b=3y , c=4z
∴(2x)2+(3y)2+(4z)3-3.2x.3y.4z
⇒8x3+27y3+64z3-72xyz

Question 20

Sol :
(i) (x+1)(x+2)(x+3)
[x(x+2)+1(x+2)](x+3)
⇒(x2+2x+x+2)(x+3)
⇒(x2+3x+2)(x+3)
⇒(x2+3x+2)(x)+(x2+3x+2)3
⇒x3+5x2+2x+3x2+9x+6
⇒x3+6x2+11x+6


(ii) (x-2)(x-3)(x+4)
⇒[x(x-3)-2(x-3)](x+4)
⇒(x2-3x-2x+6)(x+4)
⇒(x2-5x+6)(x+4)
⇒(x2-5x+6)x+(x2-5x+6)4
⇒x3-5x2+6x+4x2-20x+24
⇒x3-x2-14x+24

Question 21

Sol :
⇒Given : (x-3)(x+7)(x-4)
⇒(x(x+7)-3(x+7))(x-4)
⇒(x2+7x-3x-21)(x-4)
⇒(x2+4x-21)x-4(x2+4x-21)
⇒x3+4x2-21x-4x2-16x+84
⇒x3-37x+84

Question 22

Sol :
Given : 
⇒a2+4a+x=(a+2)2
⇒a2+4a+x=a2+2.a.2+22
⇒a2+4a+x=a2+4a+4
⇒x=a2+4a+4-a2-4a
⇒x=4

Question 23

(i) (101)2
⇒(100+1)2
⇒(100)2+2.100.1+12
⇒10000+200+1
⇒10201

(ii) (1003)2
⇒(1000+3)2
⇒(1000)2+2.1000.3+32
⇒1000000+6000+9
⇒1006009

(iii) (10.2)2
⇒(10+0.2)2
⇒(10)2+2.10×0.2+(0.2)2
⇒100+4+0.04
⇒104.04


Question 24

(i) 992
⇒(100-1)2
⇒(100)2-2.100.1+12
⇒10000-200+1
⇒9801

(ii) (9997)2
⇒(1000-3)2
⇒10002-2.1000.9+32
⇒1000000-6000+9
⇒994009
In this we used the (a-b)2
formulae i.e. (a2+2ab+b2)

(iii) (9.8)2
⇒(10-0.2)2
⇒102-2×10×0.2+(0.2)2
⇒100-4+0.4
⇒96.04

Question 25

(i) (103)3
⇒(100+3)2
∴It is in the form of 
(a+b)3=a3+3a2b+3ab2+b3
∴Here a=100 ; b=3
⇒(100)3+3.(100)2.3+33
⇒1000000+90000+2700+27
⇒1092727

(ii) 993
⇒100
⇒1000000-30000+300-1
⇒970299

(iii) (10.1)3
⇒(10+0.1)3
⇒103+3.102.(0.1)+3.10.(0.1)2+(0.1)3
⇒1000+30+3+0.01
⇒1030.301

Question 26

Sol :
Given : 2ab+c=0
⇒(2a+c)=0
Squaring both sides
⇒(2a+c)2=b2
⇒(2a)2+2.2a.c+c2=b2
⇒4a2+4ac+c2=b2
⇒4a2-b2+c2+4ac=0
Hence proved

Question 27

Sol :
⇒Given : a+b+2c=0
⇒a+b=-2c...(i)
⇒Cubing on both sides
⇒(a+b)3=(-2c)3
⇒a3+b3+3a2b+3ab2=-8c3
⇒a3+b3+3ab(a+b)=-8c3 [from (i)]
⇒a3+b3+3ab(-2c)=-8c3
⇒a3+b3-6abc=-8c3
⇒a3+b3+8c3=6abc
Hence proved

Question 28

Sol :
⇒Given a+b+c=0
⇒a+b=-c...(i)
Cubing on both sides
⇒(a+b)3=(-c)3
⇒a3+b3+3a2b+3ab2=-c3
⇒a3+b3+3ab(a+b)=-c3
⇒a3+b3+3ab(-c)=-c3
⇒a3+b3-3abc=-c3
⇒a3+b3+c3=3abc
a3+b3+c3abc=3
a3abc+b3abc+c3abc=3
a2bc+b2ac+c2ab=3

Question 29

Sol :
⇒Given x+y=4
Cubing on both sides
⇒(x+y)3=43
⇒x3+3x2y+3xy2+y3=64
⇒x3+3xy(x+y)+x3+
⇒x3+3xy(4)+y3=64
⇒x3+12xy+y3=64
⇒x3+y3+12xy-64=0

Question 30

(i) (27)3+(-17)3+(-10)3
∴If a+b+c=0; then a3+b3+c3=3abc
∴Here a=27 , b=17 , c=-10
∴27-17-10=0
∴a3+b3+c3=3abc
=3.27(-17)(-10)
=13770

(ii) (-28)3+153+133
If a+b+c=0 ; then a3+b3+c3=3abc
⇒-28+15+13=0
∴⇒a3+b3+c3=3abc
=3(-28)(15)(13)
=-16380

Question 31

Sol :
Given 86×86×86+14×14×1486×8686×14+14×14
∴It is in the form of a3+b3a2ab+b2=(a+b)
(86)3+(14)386286.14+142=86+14
=100

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