Table of Contents

## Definition

An angle measures the amount of turn

## Names of Angles

As the Angle Increases, the Name Changes:

Type of Angle | Description | Illustration |

Acute Angle | is less than 90° | |

Right Angle | is 90° exactly | |

Obtuse Angle | is greater than 90° butless than 180° | |

Straight Angle | is 180° exactly | |

Reflex Angle | is greater than 180° | |

Full Rotation | is 360° exactly |

## Positive and Negative Angles

When measuring from a line:

a positive angle goes counterclockwise (opposite direction that clocks go) | |

a negative angle goes clockwise |

## Elements of an Angle

- The corner point of an angle is called the vertex
- And the 2 straight sides are called arms
- The angle is the amount of turn between each arm.

## Labeling an Angle

There are two main ways to label angles:

- By the three letters on the shape that define the angle, with the middle letter being where the angle actually is (its vertex). Example BAC and BCD
- Give the angle a name, usually a lower-case letter like a or b, or sometimes a Greek letter like α (alpha) or θ (theta)