If $8 x^{2} - 6 x - 9 = (4 x + a) (2 x + b)$ , the value of $a$ and $b$ respectively, are

- 3, 3

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3, 3

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- 3, - 3

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3, - 3

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Solution

The correct option is B $3, - 3$
$8 x^{2} - 6 x - 9$
We have to find factors of $- 72$ so that their sum is $- 6$ .
The factors are $- 12$ and $6$ .

$∴ 8 x^{2} - 6 x - 9$ = $8 x^{2} - 12 x + 6 x - 9$
$= 4 x (2 x - 3) + 3 (2 x - 3)$
$= (2 x - 3) (4 x + 3)$

$∴ (2 x - 3) (4 x + 3) = (2 x + b) (4 x + a)$
$∴ a = 3$ and $b = - 3$

So, option D is correct.

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