Question

If $x-3$ is a factor of $x^2-ax-15,thena=$

Answer 1

Given: $x^2-ax-15$

Let, $f\left(x\right)=x^2-ax-15$

$\because x-3$ is a factor of $f\left(x\right)$, by factor theorem $f\left(3\right)=0$

$\Rightarrow (3{)}^2-a\times (3)-15=0$

$\Rightarrow 9-3a-15=0$

$\Rightarrow -3a-6=0$

$\Rightarrow a=-2$

$\because$ The value of $mis-2$.

Hence, option (A) is the correct answer.