The two congruent legs of an isosceles triangle are also called congruent sides. An isosceles triangle is a two-dimensional geometric figure containing two sides that are of equal length.
The two congruent sides of an isosceles triangle form the two base angles that are also congruent, which means that both angles have the same measure in degrees. The third interior angle of an isosceles triangle, which is the opposite angle of the base, is called the vertex angle.
The height, or altitude, of an isosceles triangle is represented by a line that divides the isosceles triangle into two equal parts, forming two right-angled triangles in the process. The two congruent sides of the isosceles triangle then form the longest sides of the two right-angled triangles.