# A triangle has sides A, B, and C. Sides A and B are of lengths 7 and 9, respectively, and the angle between A and B is (pi)/2 . What is the length of side C?

$\textcolor{w h i t e}{\times x} \sqrt{130}$
$\textcolor{w h i t e}{\times} M \left(\angle C\right) = \frac{\pi}{2} \iff {C}^{2} = {A}^{2} + {B}^{2} \textcolor{w h i t e}{\times \times x}$Pythagoras' Theorem
$\implies {C}^{2} = {\textcolor{red}{7}}^{2} + {\textcolor{red}{9}}^{2}$
$\implies C = \sqrt{49 + 81}$
$\textcolor{w h i t e}{\times x} = \sqrt{130}$