CTET 2 Math and Science Sep 2015 Paper

Question : 35 of 120

Marks: +1, -0

4x^2 + 12xy – 8x + 9y^2 – 12y

= (a x + b y) (a x + b y - 4)

, then the value of

a^2 + b^2

is:

Solution:

Given that

4 x^{2} + 12 x y - 8 x + 9 y^{2} - 12 v = (a x + b y) (a x + b y - 4)

⇒4x^{2}+12xy-8x+9y^{2}-12y

=a^{2}x^{2}+b^{2}y^{2}+2abxy-4ax-4by

Equating the coefficient of

x^2

and

y^2

,we get

4x^{2}=a^{2}x^{2};9y^{2}=b^{2}y^{2}

∴a^2=4\;\;\;\;∴b^2=9

Now,

a^{2}+b^{2}=4+9=13

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