Answer
$x^2+64=0$
Work Step by Step
As we are given that solution set : {$-8i,8i$}
This implies that $x=-8i,8i$
As per zero-product reverse property, we have $(x+8i)(x-8i)=0$
Now, apply FOIL METHOD
$(x+8i)(x-8i)=0\implies x^2-(8i)^2=0$
or, $x^2+64=0$
