Definitions and Examples

This page shows the different types of angles and their names: acute, right, obtuse, straight, and reflex.

Two line segments that share a common endpoint form an angle. The common point (looks like the "corner") is called the vertex.

The figure to the right shows an angle. The angle is called "Angle CAB" and is written $\angle{CAB}$ because it is made up of the three points C, A, and B. The angle could also be called $\angle\,BAC$ . Note that in both ways to name the angle the A is in the middle because it is the vertex.

The green arc betwen the two line segments is the angle and is used to highlight the distance between the two sides of the angle.

Directions:

Move point C and notice how the degrees change. As the degrees change, the type of angle will also change.
You will see that there are five types of angles: acute, right, obtuse, straight, and reflex.

Duane Habecker, 03/14/2010, Created with GeoGebra

Acute Angle
	An ACUTE ANGLE is one whose measure is LESS THAN 90 DEGREES. Notice $\angle~ABC$ does not quite reach 90 degrees... acute angles are always less than 90 degrees.
Right Angle
	A RIGHT ANGLE is an angle whose measure is EXACTLY 90 DEGRRES. Right angles are denoted by a small square in its interior.
Obtuse Angle
	An OBTUSE ANGLE is one whose measure is GREATER THAN 90 AND LESS THAN 180 DEGREES.
Straight Angle
	A STRAIGHT ANGLE is one whose measure is EXACTLY 180 DEGREES. A straight angle is made up of two opposite rays or line segments. Another important fact is that a straight angle forms a straight line.
Reflex Angle
	A REFLEX ANGLE is one whose measure is GREATER THAN 180 AND LESS THAN 360 DEGREES.