Question

The interior of a regular polygon is 140 degrees. Find the sum of the polygon

Answer 1

`\underset{in~degrees}{\textit{sum of all interior angles}}\\\\ n\theta = 180(n-2) ~~ \begin{cases} n=\stackrel{number~of}{sides}\\ \theta = \stackrel{degrees}{angle}\\[-0.5em] \hrulefill\\ \theta =140 \end{cases}\implies n140=180n-360 \\\\\\ 140n+360=180n\implies 360=40n\implies \cfrac{360}{40}=n\implies 9=n \\\\[-0.35em] ~\dotfill\\\\ \stackrel{ their~sum }{(9)(140)}\implies \text{\LARGE 1260}`