Answer
The solutions are $4$ and $-4$.
Work Step by Step
$ 5x^{2}=80\qquad$ ...divide each side with $5$.
$ x^{2}=16\qquad$ ...take square roots of each side.
$\sqrt{x^{2}}=\sqrt{16}\qquad$ ...simplify.
...When solving an equation of the form $x^{2}=s$ where $s>0$,
we find both the positive and negative solutions.
$x=\pm 4$
