• ### 30-60-90 Triangle

A triangle with a 30, 60, and 90 degree angle.

• ### 45-45-90 Triangle

A triangle with a two 45 degree angles and one 90 degree angle.

• ### Acute Triangle

A triangle with three acute angles.

• ### Base Angle

An angle of an isosceles triangle opposite one of the equal sides, i.e. opposite one of the legs.

• ### Base of an Isosceles Triangle

The side of an isosceles triangle unequal to the other two sides, the legs.

• ### Equiangular Triangle

A triangle whose angles are all equal.

• ### Equilateral Triangle

A triangle whose sides are all equal (of equal length).

• ### Hypotenuse

The side of a right triangle opposite the right angle. The Pythagorean Theorem states that the square of the hypotenuse is equal to the sum of the square of the other two sides.

• ### Isosceles Triangle

A triangle with at least two equal sides.

• ### Legs of a Right Triangle

The two sides of a right triangle opposite the two oblique angles.

• ### Legs of an Isosceles Triangle

The two sides of an isosceles triangle that are equal.

• ### Obtuse Triangle

A triangle with one obtuse angle.

• ### Pythagorean Theorem

The theorem that states that the length of the hypotenuse squared is equal to the sum of the squares of the lengths of the legs of a right triangle; c2 = a2 + b2.

• ### Pythagorean Triple

A set of three integers a, b, and c such that c2 = a2 + b2

• ### Right Triangle

A triangle with one right angle.

• ### Scalene Triangle

A triangle with no equal sides.

• ### Vertex Angle

The angle in an isosceles triangle opposite the base.

• ### Formulae

 Length of Hypotenuse c = a2 + b2), where a and b are the lengths of the legs.

 Length of a Leg a = c2 - b2), where c is the length of the hypotenuse and b is the length of the other leg.