#### Answer

$c=\pm2\sqrt{2}$

#### Work Step by Step

$x^2=a$ implies $x=\pm\sqrt{a}$ (the Square Root Principle).Therefore, the solutions to the given equation, $
c^2-8=0
,$ are
\begin{array}{l}\require{cancel}
c^2=8
\\\\
c=\pm\sqrt{8}
\\\\
c=\pm\sqrt{4\cdot2}
\\\\
c=\pm\sqrt{(2)^2\cdot2}
\\\\
c=\pm2\sqrt{2}
.\end{array}