[tex]\bf \textit{sum of all interior angles in a polygon}\\\\
\stackrel{sum}{\theta n}=180(n-2)\quad
\begin{cases}
\theta =angle~in\\
\qquad degrees\\
n=\textit{number of sides}\\
---------\\
n=8
\end{cases}\implies \theta 8=180(8-2)
\\\\\\
\theta 8=180(6)\implies \theta 8=1080\implies \theta =\cfrac{1080}{8}\implies \theta =135[/tex]
