IM Commentary. The division of triangles into scalene, isosceles, and equilateral can be thought of in terms of lines of symmetry. A scalene triangle is a triangle with no lines of symmetry while an isosceles triangle has at least one line of symmetry and an equilateral triangle has three lines of symmetry. This activity provides students an opportunity to recognize these distinguishing features of the different types of triangles before the technical language has been introduced.