Theory explained in text

Some triangles have special properties with makes them unique.

Isosceles triangle is a triangle with at two equal legs (sides). In triangle ABC given below, sides AB and AC are equal, and we call those legs. BC is the base.
The angles at the base are called the base angles and are the same

Isosceles Triangles ( Read ) | Geometry | CK-12 Foundation

 

An equilateral triangle is a triangle with all three sides of equal length. It has 3 lines of symmetrie and has rotational symmetrie of 360o : 3 = 120o. The angles of a equailateral triangle are all 60o.
Equilateral triangle - Wikipedia

 

A right-angled triangle is a triangle in which one angle is a right angle (90o). Your protractor triangle is a right-angled triangle.

Right triangle - Simple English Wikipedia, the free encyclopedia