Prime objective of this lecture is to present on Classifying Triangles. Two Ways to Classify Triangles: By Their Sides and By Their Angles. Classifying Triangles By Their Sides: Scalene and Isosceles. Classifying Triangles By Their Angles: Acute, Right and Obtuse. All of each may be of different or the same sizes; any two sides or angles may be of the same size; there may be one distinctive angle. The types of triangles classified by their sides are the following: Equilateral triangle: A triangle with all three sides equal in measure.