#### Answer

$x=\pm2$

#### Work Step by Step

Using the properties of equality, the given equation, $
5x^2=20
,$ is equivalent to
\begin{array}{l}\require{cancel}
x^2=\dfrac{20}{5}
\\\\
x^2=4
.\end{array}
Taking the square root of both sides, then the solutions of the given equation are
\begin{array}{l}\require{cancel}
x=\pm\sqrt{4}
\\\\
x=\pm\sqrt{(2)^2}
\\\\
x=\pm2
.\end{array}