## The Lesson

An angle is created by two rays that have a common end point, called the vertex.The angle is also a measure of the rotation between the two rays. Angles can be measured in degrees (°) or in radians.

## How to Identify an Angle

Angles are often identified using Greek letters (α, β, γ, θ, ψ). The letter theta θ is often used.In geometric figures, points are often labelled with capital letters. Consider the angle made between points ABC, where the vertex is A and AB and AC are the rays:

The angle can be identified as the angle A, or by ∠BAC, where the middle of the 3 letters is the vertex.

## How to Measure an Angle

An angle is measured by the shortest rotation between the two rays. Angles are often measure in degrees, denoted °. There are 360 degrees in a full rotation. Angles can also be measured in radians. There are 2π radians in a full rotation. Angles can be measured directly using a protractor:Angles can also be calculated using geometry and trigonometry.

## Types of Angles

The different types of angles are:Type of Angle | Description | |
---|---|---|

Acute | Less than 90° | |

Right | 90° | |

Obtuse | Greater than 90° but less than 180° | |

Straight | 180° | |

Reflex | Greater than 180° | |

Full | 360° |

## Interactive Game on the Types of Angles

## Parts of an Angle

An angle is created by two rays meeting at a common endpoint, the vertex.-
A
**ray**is a line which starts from a point. -
A
**vertex**is the point where the two rays meet.