What is the sum of the measures of the interior angles of an octagon?
In the figure above we have an irregular octagon
5 diagonals each originating from A are drawn.These diagonals divide the octagon into 6 triangles.
It is obvious from the figure that the sum of the measures of the interior angles of the octagon is equal to the sum of the interior angles of 6 triangles.
As we know that sum of the interior angles of a triangle is
Comparing with this situation we can say that a polygon of n-sides can be divided into
How will you get the sum of 8 interior angles of a concave irregular octagon using following figure?