To find the sum of interior angles in a polygon divide the polygon into triangles. The sum of interior angles in a triangle is 180°. To find the sum of interior angles of a polygon, multiply the number of triangles in the polygon by 180°. A polygon is a closed geometric figure whose sides are simple line segments. Each corner of a polygon where two sides intersect is called a vertex of the polygon. For example, a triangle is a polygon with 3 sides. There are also three vertices, one at each point.
