Find the sum of interior angles of a parallelogram.
180 o
360o
540o
240o
Sum of interior angle = (n-2) × 180∘
Where n is the number of sides in a polygon
Parallelogram has 4 sides, so n = 4
Sum of interior angle = (2) × 180∘ = 360∘
We know that the sum of the interior angles of a triangle is 180∘. 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 for a 21 sided polygon.