If you wondered why is the angle sum of a triangle is 180 degrees, why is the formula of finding the angle sum of a polygon with n sides is 180(n-2), then this series is for you. 

The Angle Sum Series

• Proof that the Triangle Angle Sum is 180 Degrees
• Proof that the Quadrilateral Angle Sum is 360 Degrees
• The Polygon Angle Sum Proof
• Proof of Sum of the Exterior Angles of a Polygon

Note that all these videos are in Taglish.