If the value of $x^{2} - a x - 12$ is 20 at $x = 4$ , then find the value of $a$ .

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-2

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Solution

The correct option is C -4
Value of exprssion $x^{2} - a x - 12$ is 20 at $x = 4$ .
So, let's first put $x = 4$ in the given expression.
$⟹ 4^{2} - a \times 4 - 12 = 20 ⟹ 16 - 4 a - 12 = 20 ⟹ 4 - 4 a = 20 ⟹ - 4 a = 20 - 4 = 16 ⟹ a = - 4$

Hence, option 'c' is correct.

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