Prove that the sum of the interior angles of an octagon is twice the sum of interior angles of a pentagon

The sum of all interior angles of a hexagon is

The sum of co interior angles is

Sum of interior angles of polygon

Prove that sum of all the interior angles of a pentagon is 540^@ .

In a convex hexagon, prove that the sum of all interior angle is equal to twice the sum of its exterior angles formed by producing the sides in the same order.

In a convex hexagon,prove that the sum of all interior angle is equal to twice the sum of its exterior angles formed by producing the sides in the same order.

We know that the sum of the interior angles of a triangle is 180^0 . Show that the sums of the interior angles of polygons with 3,4,5,6 sides form an arithmetic progression. Find the sum of the interior angles of a 21 sided polygon.

We know that the sum of the interior angles of a triangle is 180^0 . Show that the sums of eth interior angles of polygons with 3,4,5,6, sides for an arithmetic progression. Find the sum of the interior angles of or a 21 sided polygon.