<Ul> <Li> An equilateral triangle has all sides the same length . An equilateral triangle is also a regular polygon with all angles measuring 60 ° . </Li> <Li> An isosceles triangle has two sides of equal length . An isosceles triangle also has two angles of the same measure , namely the angles opposite to the two sides of the same length ; this fact is the content of the isosceles triangle theorem , which was known by Euclid . Some mathematicians define an isosceles triangle to have exactly two equal sides , whereas others define an isosceles triangle as one with at least two equal sides . The latter definition would make all equilateral triangles isosceles triangles . The 45 -- 45 -- 90 right triangle , which appears in the tetrakis square tiling , is isosceles . </Li> <Li> A scalene triangle has all its sides of different lengths . Equivalently , it has all angles of different measure . </Li> </Ul>
what are the three types of triangles classified by sides
equilateral triangle isosceles triangle scalene triangle