# Angles

## 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)