#### Answer

$x=\pm10$

#### Work Step by Step

Since $x^2=a$ implies $x=\pm\sqrt{a}$ (the Square Root Principle), then the solutions to the given equation, $
x^2=100
,$ are
\begin{array}{l}\require{cancel}
x=\pm\sqrt{100}
\\\\
x=\pm\sqrt{(10)^2}
\\\\
x=\pm10
.\end{array}