SSC CGL Tier II 1 Dec 2016 Paper 1

Question : 71 of 100

Marks: +1, -0

x^{4}+2 x^{3}+a x^{2}+b x+9

is a perfect square, where a and b are positive real numbers, then the values of a and b are

Solution:

(3)

(a+b+c)^{2}

=a^{2}+b^{2}+c^{2}+2 a b+2 a c+2 b c

∴(x^{2}+x+3 )^{2}

=x^{4}+x^{2}+9+2 x^{3}+6 x+6 x^{2}

=x^{4}+2 x^{3}+7 x^{2}+6 x+9

On comparing with

x^{4}+2 x^{3}+ a x^{2}+b x+9

a=7, b=6

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