The lengths and angles of similar triangles will depend on the types of triangles that they are. The three types of triangles are: equilateral, isosceles and scalene. An equilateral triangle, is also known as a regular polygon and has sides that are all equal in length. The angles of an equilateral triangle, also all measure 60 degrees. An isosceles triangle has two sides of equal length, and also two angles of the same measure. In an isosceles triangle these equal angles are opposite the two sides of equal length. A scalene triangle has sides that are all different lengths, and so also angles that are all of a different measure. Triangles can also be classified by the measure of their internal angles: a right triangle has one of its internal angles measuring 90 degrees, oblique triangles do not have a 90 degree internal angle, acute triangles have all internal angles measuring less than 90 degrees, and an obtuse triangle will have one internal angle measuring more than 90 degrees.