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Question

The HCF of the functions
x3+(a+b)x2+(ab+1)x+b and x3+2ax2+(a2−1)x+a is

A
x2+ax+1
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B
x2+bx+1
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C
x2+x+a
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D
x2+x+b
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Solution

The correct option is A x2+ax+1
x3 + (a +b)x2 + (ab + 1)x + b
= x3 + (a +b)x2 + abx + x + b
= x [x2 + (a + b)x + ab] + (x + b)
= x (x + a) (x + b) + (x + b)
= (x + b) [x (x + a) + 1]
= (x + b) (x2 + ax + a)

x 3 + 2ax 2 + (a 2 + 1)x + a
= x3 + 2ax2 + a 2 x + x + a
= x (x 2 + 2ax + a 2 ) + (x + a)
= x (x + a) (x + a) + (x + a)
= (x + a) [x (x + a) + 1]
= (x + a) (x 2 + ax + 1)
Common factor between the two polynomials = x 2 + ax + 1
∴ HCF = x 2 + ax +1

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