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

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Solution

The correct option is C
- 1

Given $(3 x - 4) (5 x + 7) = 15 x^{2} - a x - 28$
$\Rightarrow 15 x^{2} - 20 x + 21 x - 28 = 15 x^{2} - a x - 28$
$\Rightarrow 15 x^{2} + x - 28 = 15 x^{2} - a x - 28$

On comparing the coefficient of $x$ on both the sides, we get
$- a = 1$
So, $a = - 1$

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