Question

If $4$ is a root of a quadratic equation $x^2+ax-8=0$ then $a=$ _____

• A. $2$
• B. $4$
• C. $-2$
• D. $-4$

Answer 1

The correct option is C $-2$

$\begin{array}{c}p\left(x\right)=x^2+ax-8=0\\ p\left(4\right)={\left(4\right)}^2-8+4a=0\\ 16-8+4a=0\\ 8+4a=0\\ 4a=-8\\ a=-2\end{array}$