Isosceles triangle theorem
If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
Corollary 1: An equilateral triangle is also equiangular
Corollary 2: An equilateral triangle has three 60 degree angles
Corollary 3: The bisector of the vertex angle of an isosceles triangle is perpendicular to the base ate its midpoint