How can triangles be classified by sides?

Answer 1

There are three ways to classify a triangle by its sides:

A scalene triangle is a triangle where no two sides are of the same length. That is, all three sides are different lengths

An isosceles triangle is a triangle where at least two sides have equal length. (Note: In some textbooks, they define an isosceles as having exactly two sides with equal length).

An equilateral triangle has all three sides with equal lengths. By the first definition for isosceles, this means that an equilateral triangle would also be isosceles. It all depends on the book being used.