Are triangles polygons?

As you learned in the last lesson, a triangle is the simplest polygon, having three sides and three angles. The sum of the three angles of a triangle is equal to 180 degrees. Triangles are classified by sides and by angles. Move your cursor over the triangles to learn more. read more

In triangle ABC below, all sides are 12 feet making triangle ABC equilateral. A regular polygon is BOTH equiangular and equilateral. A square is a regular polygon because all sides have the same length and all angles measure the same: 90 degrees. read more

The "inside" circle is called an incircle and it just touches each side of the polygon at its midpoint. The radius of the incircle is the apothem of the polygon. (Not all polygons have those properties, but triangles and regular polygons do). read more