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)