What Are Equilateral Triangles?

Equilateral triangles have three equal sides and angles

Equilateral triangles are the "opposite" of scalene triangles. When all of a triangle's sides are of equal length and all of its angles have a measure of $60^\circ$, it is considered equilateral. You could also say equiangular, since the three angle measures are all the same ($60^\circ$).

The triangle below is an equilateral triangle. Notice that all the sides have equal length (shown by the small marks growing across them) and all the angles are congruent.

Properties of equilateral triangles

• Since all triangles' angles have to add up to $180^\circ$, you can actually determine that a triangle is equilateral by knowing that just two of its angles are $60^\circ$.

• Equilateral triangles have three lines of symmetry: one for each altitude.
• Each altitude on an equilateral triangle is also one of the triangles' medians.