You'll be using Sketch 1 of this file which has three different types of triangles - scalene, isosceles, equilateral. Each triangle type has a different colour (pink for scalene, red for equilateral, ...

Named for Plato, who theorized that the classical elements were made of these regular polyhedrons, three of the Platonic solids are composed of equilateral triangles: the tetrahedron, octahedron ...