This document defines angles and different types of angles using degrees of rotation. An angle is measured by the amount of turning from one line to another around a common point called the vertex. There are five main types of angles: acute angles less than 90 degrees, right angles equal to 90 degrees, obtuse angles between 90 and 180 degrees, straight angles equal to 180 degrees, and reflex angles greater than 180 degrees. Key terms defined include degree, vertex, quarter turn, half turn, three-quarter turn, and full turn.

1. Review of Angles
90˚ 180˚ 270˚ 360˚
Angles are a measure of the amount, or degree of turning from one
line to another around a common point, called the vertex.
degree
vertex
Quarter Turn Half-Turn
Three-Quarter Turn Full-Turn
REMEMBER: a right angle is 90˚.

2. Important Vocabulary
90˚
Copy the above angle and vocabulary into your notebook.
Degree (a measure
for angles)
Vertex
(an endpoint
where two
line segments
or lines come
together)
90˚ = Right Angle

3. Types of Angles
Type of Angle Description
Acute Angle An angle that is less than 90˚
Right Angle An angle that is exactly 90˚
Obtuse Angle An angle that is greater than 90˚ but less than 180˚
Straight Angle An angle that is 180˚ exactly
Reflex Angle An angle that is greater than 180˚
Full Rotation 360˚
Copy the chart above into your notebook.