Interior angles of polygons
An interior angle is an angle that lies inside a polygon.
You can use the sum of the angle measures of a triangle to find the sum of the interior angle measures of various polygons.
Number of sides 
Sketch of figure 
Number of triangles 
Sum of Angle Measures 
3 
Triangle

1 
1(180º)=180º 
4 
Quadrilateral 
2 
2(180º)=360º 
5 
Pentagon 
3 
3(180º)=540º 
6 
Hexagon 
4 
4(180º)=720º 
INTERIOR ANGLE SUM OF A POLYGON
The sum of the measures of the interior angles of a polygon is (n2)180, where n represents the number of sides.
S=(n2)180
Find the sum of the measures of the interior angles of a decagon.