Exercise 4(H)
Question 1
a³ + 1
Sol :
=x3+1
=(x)3+(1)3
=(x+1)(x2−x+1)
Question 2
x³ + 8
Sol :
Question 3
8x³ + 1
Sol :
Question 4
x³ – 27
Sol :
Question 5
a³ – 8
Sol :
=a3−8
=(a)3−(2)3
=(a−2)[(a)2+a×2+(2)2]
=(a−2)(a2+2a+4)
Question 6
27m³ – 8
Sol :
Question 7
x³+ 64
Sol :
Question 8
8a3−b6
Sol :
Question 9
x6+8b3
Sol :
Question 10
8a³ + 21b³
Sol :
Question 11
27x³ – 8y³
Sol :
Question 12
128x³ + 2
Sol :
Question 13
Factorise :
8x3–127y3
Sol :
Question 14
343x3y+512y4
Sol :
=343x3y+512y4
=y(343x3+512y3)
=y[(7x)3+(8y)3]
=y[(7x+8y)[(7x)2−7x×8y+(8y)2]]
=y(7x+8y)(49x2−56xy+64y2)
Question 15
(2a + b)³ + (a + 2b)³
Sol :
=(x+y)(x2−xy+y2)
=(2a+b)3+(a+2b)3=(2a+b+2b)
=[(2a+b)2−(2a+b)(a+2b)+(a+2b)2]
Question 16
27 (m + 2n)³ + (m – 6n)³
Sol :
=(3a+b)[(3a)2−3ab+(b)2]
=(3a+b)(9a2−3ab+b2)
Question 17
8 (a + b)³ – 21c³
Sol :
Question 18
x6−1
Sol :
=x6−1
=(x3)2−(1)2
=(x3+1)(x3−1)
=[(x)3+(1)2][(x)3−(1)3]
=(x+1)(x2−x+1)(x−1)(x2+x+1)
=(x+1)(x−1)(x2−x+1)(x2+x+1)
Question 19
Sol :
=(8a3+b3)(8a3−b3)
=[(2a)3+(b)3][(2a)3−(b)3]
=(2a+b)[(2a)2−2a×b+(b)2](2a−b)[(2a)2+2a×b+b2]
=(2a+b)(4a2−2ab+b2)(2a−b)(4a2+2ab+b2)
=(2a+b)(2a−b)(4a2+2ab+b2)(4a2−2ab+b2)
Question 20
a³ – b³ + 4 (a – b)
Sol :
=a3−b3+4(a−b)=(a−b)(a2+ab+b2)+u(a−b)=(a−b)(a2+ab+b3+4)
Question 21
x3−1x3−6x+6x
Sol :
=x3−1x3−6x+6x=(x−1x)(x2+1+1x2)−6(x−1x)=(x−1x)(x2+1+1x2−6)=(x−1x)(x2−5+1x2)
Question 22
64a³ + 125b³ + 12a²b + 15ab²
Sol :
=64a3+125b3+12a2b+15ab2=[(4a)3+(5b)3]+3ab(4a+5b)=(4a+5b)[(4a)2−4a×5b+(5b)2]+3ab(4a+5b)
=(4a+5b)(16a2−20ab+25b2)+3ab(4a+5b)
=(4a+5b)(16a2−20ab+25b2+3ab)
=(4a+sb)(16a2−17ab+25b2)
Question 23
375 (a – b)³+ 3
Sol :
=375(a−b)3+3
=3[125(a−b)3+1]
=3[{5(a−b)y3+(1)3]
=3[{5(a−b)+1}{(5(a−b)}2−5(a−b×1+(1)2]
=3[(5a−5b+1)(25(a2+b2−2ab)−5a+5b+1)]
=3(5a−5b+1)(25b2−50ab−5a+5b+1)
Question 24
a4+b4=a2b2 , Show that a6+b6=0
Sol :
a4+b4=a2b2
L.H.S
=a6+b6=(a2)3+(b2)3
=(a2+b2)[a4−a2b2+b4]
=(a2+b2)(a4+b4−a2b2)
=(a2+b2)(a2b2−a2b2)
a4+b4=a2b2 already given
=(a2+b2)×0=0
R.H.S
L.H.S=R.H.S
Nice
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