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) (3x−12x)2
It is in the form of (a−b)2=a2−2ab+b2
Here, a=3x ; b=12x
(3x)2−2.3x.12x+(12x)2
32−x2−3+122x2
9x2−3+14x2
(ii) (12x−32y)2
It is in the form of (a−b)2=a2−2ab+b2
Here, a=12x ; b=32y
∴(12x)2−2×1x2×32y+(32y)2
x24−3xy2+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+3x−1)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(6−3x−2x)
⇒4x2+9x2+1+12−6x−4x
⇒4x2+9x2−6x−4x+13
(ii) (23x−32x−1)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)]
⇒49x2−94x2+1+2[−1+32x−23x]
⇒49x2−94x2+1+2+62x−4x3
⇒49x2−94x2+3x−4x3−1
Question 7
(i) (x+2)3
Sol :
It is in the form of (a+b+c)2=a2+b2+c2+2(ab+bc+ca)
⇒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) (2x−13y)3
Sol :
⇒(2x)3−3.(2x)2.13y+3.2x.(13y)2−(13y)3
⇒8x3−3.4x2.13y+3.2x.19y2−127y3
⇒8x3−4x2y+2x3y2−127y3
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+(a−1a)2
⇒(a2+2.a.1a+)+(a2+2.a.1a+1a2)
⇒a2+2+1a2+a2−2+1a2
⇒2a2+2a2
⇒2(a2+1a2)
(ii) (a+1a)2−(a−1a)2
⇒(a2+2.a.1a+1a2)−(a2−2.a.1a+1a2)
⇒a2+2+1a2−a2+2−1a2
⇒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) (2x−3x)(2x+3x)
⇒(2x)2−(3x)2
⇒(2x)2−(3x)2
⇒Since it is in the form of (a+b)(a-b)=a2-b2
∴ 4x2−9x2
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
Question 15
Question 16
Question 17
Question 18
⇒27p3-64q3
Question 19
Question 20
Question 21
Question 22
Question 23
Question 24
Question 25
Question 26
Question 27
Question 28
⇒a3abc+b3abc+c3abc=3
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