Polygons and figures. Triangles

Plane figures are flat. They can be closed or not closed.

Plane figures made up of three or more closed line segments are polygons. Each line segment of a polygon is a side. Polygons are classified by the number of sides. 

A triangle has three sides. There are different kinds of triangles.

• An equilateral triangle has three sides of equal length.
• An isosceles triangle has only two sides of equal length.
• A right triangle has one right angle.

How many triangles can you see?