We can relate the sum of the interior angles of a polygon S with its number of sides n as:
[tex]S=(n-2)\cdot180[/tex]Then, if S=1980 degrees, we can find n as:
[tex]\begin{gathered} 1980=(n-2)\cdot180 \\ n-2=\frac{1980}{180} \\ n-2=11 \\ n=11+2 \\ n=13 \end{gathered}[/tex]Answer: the polygon has 13 sides (n=13)
