An equilateral triangle is a triangle whose sides are all equal. It is a
specific kind of isosceles triangle whose base is equal to
each leg,
and whose vertex angle is equal to its base angles.
You may have already noticed from the figure above that the angles of an
equilateral triangle are all equal. This is true because of the special
property of isosceles triangles. Every equilateral triangle is also an
isosceles triangle, so any two sides that are equal have equal opposite angles.
Therefore, since all three sides of an equilateral triangle are equal, all three
angles are equal, too. Hence, every equilateral triangle is also
equiangular.