Answer
$\lbrace 10,-10\rbrace.$
Work Step by Step
We need to solve the following quadratic equation by square root method $x^{2}=100.$
Consider,
\begin{align*}
x^{2}&=100\\
x&= \pm\sqrt{100}\\
x&=10 \ \ \text{or} \ \ x=-10.
\end{align*}
Hence, the solution set is $\lbrace 10,-10\rbrace.$
