Introduction: Have you ever played a game of pool? If so, you have experimented with angles! Pool players use angles when deciding which target ball to hit with the white cue ball. How the cue ball is hit will control where the target and cue balls go. If the cue ball is hit perfectly and doesn't spin, it will bounce off the target ball at a right angle. A good pool player will use this knowledge to change how she hits the cue ball. A well hit and angled shot will send the target ball into the pocket and setup the next shot for the player.

An angle is formed when two lines or rays meet at the same endpoint. The distance between the rays is measured in degrees. In geometry, we can measure the number of degrees for an angle using a protractor. However, sometimes we just need to describe the general shape of the angle, not give an exact measurement. To do so, we classify angles by types. An acute angle measures less than [math]90deg[/math]. It looks narrow. A right angle is exactly [math]90deg[/math]. It looks like the corner where two walls meet. An obtuse angle measures more than [math]90 deg[/math] but less than [math]180 deg[/math]. It looks wide. A straight angle measure [math]180deg[/math]. It is a line. A reflex angle is more than [math]180deg[/math] and less than [math]360deg[/math]. It opens wider than a straight angle, but does not make a full circle. The table shows the definitions and examples of the angle types.

 

Types of Angles
Name	Example	Definition
Acute		[math]<90deg[/math]
Right		[math]90deg[/math]
Obtuse		[math]>90deg and <180deg[/math]
Straight		[math]180deg[/math]
Reflex		[math]>180deg and <360deg[/math]