If $(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28$ then $a =$ ____

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-1

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-2

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none of these

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Solution

The correct option is B -1
Hence,
$(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28$
$\Rightarrow 15 x^{2} + 21 x - 20 x - 28 = 15 x^{2} - a x - 28$
$\Rightarrow 15 x^{2} + x - 28 = 15 x^{2} - a x - 28$
Equating the terms having similar powers:-
$\Rightarrow x = - a x$
$\Rightarrow a = - 1$
$\Rightarrow$ Option B is correct.

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(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28

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