Be sure you know not just the definitions of these triangle types but, more
importantly, their special characteristics: side relationships, angle
relationships, and area formulas.
Isosceles triangle: An isosceles triangle is a triangle that has two equal sides.
Not only are two sides equal, but the angles opposite the equal sides, called
base angles, are also equal.
Equilateral triangle: An equilateral triangle is a triangle that has three equal
sides. Since all the sides are equal, all the angles are also equal. All three
angles in an equilateral triangle measure 60 degrees, regardless of the lengths
of the sides. You can find the area of an equilateral triangle by dividing it into
two 30-60-90 triangles, or you can use this formula in terms of the length of
one side s:
Right triangle: A right triangle is a triangle with a right angle. The two sides
that form the right angle are called legs, and you can use them as the base
and height to find the area of a right triangle.
THREE SPECIAL TRIANGLE TYPES
1. Isosceles: Two equal sides and two equal angles.