# Angle

An angle is defined as the amount of rotation between two rays. There are two systems for measuring angles in mathematics: degrees and radians. A full rotation in degrees is . A full rotation in radians is (tau) radians or approximately radians. For higher level math, radians are the preferred system to measure angles[1].

## Types of Angles

Acute Angle | Concept

An acute angle is an angle that is smaller than 90 degrees or PI fourths.

Obtuse Angle | Concept

An obtuse angle is an angle that is larger than 90 degrees or PI fourths.

Perpendicular Angle | Concept

A Perpendicular angle, sometimes also referred to as a square angle, is exactly 90 degrees or PI fourths.

## Related Angles

Complementary Angles | Notation

Complementary angles can visually be denoted as two angles who sum to a perpendicular or square angle.

Supplementary Angles | Notation

Supplementary angles can visually be denoted as two angles who sum to 180 degrees or PI degrees.

## Degrees

The degree angle system divides a full rotation into degrees.