Calculate the value of $9 x^{2} - 42 x y + 49 y^{2}$ given that $3 x - 7 y = 8$ .

\sqrt{8}

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16

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64

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128

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Solution

The correct option is C $64$
Given, $3 x - 7 y = 8$
Squaring both the sides, we get
$\Rightarrow (3 x - 7 y)^{2} = 8^{2}$
$\Rightarrow 9 x^{2} - 42 x y + 49 y^{2} = 64$ ........By $(a - b)^{2} = a^{2} - 2 a b + b^{2}$

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Similar questions

9 x^{2} + 49 y^{2} - 42 x y

x = 15

y = 3

9 x^{2} + 49 y^{2} - 42 x y

x = 15

y = 3

$I f 3 x - 7 y = 10 a n d x y = - 1, f i n d t h e v a l u e o f 9 x^{2} + 49 y^{2}$

3 x - 7 y = 10

x y = - 1

9 x^{2} + 49 y^{2}

8, 7, 16, 5, 32, 3, 64, 1, 128, (?)

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