Acute angle
An angle whose measure is greater than 0 but less than 90 degrees.

Acute triangle
A triangle whose angles are acute.

Cosine
Ratio determined by the hypotenuse in a right triangle and a side adjacent to a reference angle.

Equilateral triangle
A triangle whose sides are equal in length.

Isosceles triangle
A triangle with two sides of equal length.

Proportion
A statement that two ratios are equal

Proportional
One of four numbers that form a true proportion

Sine
Ratio of the length of the opposite side to a reference angle in a right triangle and the hypotenuse. Opposite/hypotenuse.

Obtuse angle
An angle whose measure is greater than 90 but less than 180 degrees

Obtuse triangle
A triangle with one acute angle.

Ratio
A quotient of 2 numbers

Right triangle
A triangle that has a 90 degree angle.

Scalene triangle
A triangle with no equilateral sides.

Triangle
A polygon with three sides.