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