CTET 2 Math and Science Sep 2016 Paper

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Question : 50 of 150

Marks: +1, -0

When

x =1/9

and

y = -3/4

, then the value of the expression

81x^2 +16y^2 – 72xy

is :

$9 /4$
$9 /16$
25
16

Solution:

Consider the expression

81x^{2}+16y^{2}-72xy

Now, the value of expression of

x=\;\;{1}/{9},y=-\;\;{3}/{4}

is
Then,

81x^{2}+16y^{2}-72xy=81(\;\;{1}/{9})^{2}+16(-\;\;{3}/{4})^{2}-72(\;\;{1}/{9})(-\;\;{3}/{4})

=81×\;\;{1}/{81}+16×\;\;{9}/{16}+72(\;\;{1}/{9})(\;\;{3}/{4})

=1+9+6

=16

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