If $a^{2} + b^{2} = 34$ and $a b = 12$ , find : $7 (a - b)^{2} - 2 (a + b)^{2}$ .

186

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46

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- 46

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- 186

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Solution

The correct option is A $- 46$
Given, $a^{2} + b^{2} = 34$ , $a b = 12$
Now,
$7 (a - b)^{2} - 2 (a + b)^{2}$
$= 7 (a^{2} + b^{2} - 2 a b) - 2 (a^{2} + b^{2} + 2 a b)$
$= 7 (34 - 2 \times 12) - 2 (34 + 2 \times 12)$
$= 7 (34 - 24) - 2 (34 + 24)$
$= 70 - 116$
$= - 46$

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