It's possible to demonstrate and prove mathematically that the angle sum of every triangle is 180 degrees. The techniques used are useful for solving all kinds of other geometry problems too.

Discusses the properties and types of triangles, explaining that a triangle is a closed figure with three sides and angles ... the importance of triangles in mathematics, architecture, and ...

Polygons can be regular or irregular. If the angles are all equal and all the sides are equal length it is a regular polygon. To find the sum of interior angles in a polygon divide the polygon ...