An isosceles triangle is a triangle with at least two congruent
sides; that is to say, at least two sides are exactly the same
length. This will mean that it also has two congruent
(identical) angles, and it is bilaterally symmetrical. An
equilateral triangle is a special case of the isosceles
triangle, in which all three sides are the same length, and all
of its internal angles are also the same, 60°. These are in
contrast to scalene triangles, in which all sides are different
lengths. When only two sides are equal, it is traditional to
refer to the unequal side as the base of the triangle. This puts
the odd angle out at the top, making it the vertex angle. The
vertex will be centered directly over the midpoint of the base.
The right isosceles triangle (AKA the 45-45-90 triangle) is one
of the most commonly seen triangles, and is used widely in
architecture and engineering. It has one right angle (90°), and
two 45° angles. This is the only right triangle that is also an
isosceles triangle. Isosceles comes fr