Answer :
[tex]\bf \textit{sum of all interior angles of a regular polygon}
\\\\\\
n\theta=180(n-2)\qquad
\begin{cases}
n=\textit{number of sides in the polygon}\\
\theta=\textit{one internal angle}
\end{cases}
\\\\\\
\theta=\cfrac{180(n-2)}{n}[/tex]