Answer
$m=\sqrt{n^2+p^2}$
Work Step by Step
Using $a^2+b^2=c^2$ or the Pythagorean Theorem, the relationship of the sides of the given right triangle is
\begin{align*}
n^2+p^2&=m^2
\\
m^2&=n^2+p^2
.\end{align*}
Taking the square root of both sides (Square Root Property), the equation above is equivalent to
\begin{align*}
m&=\pm\sqrt{n^2+p^2}
.\end{align*}
Since $m$ should be greater than zero, then
\begin{align*}
m&=\sqrt{n^2+p^2}
.\end{align*}
