# Chapter 9 Angles

• Chapter 9

Chapter Objective:

* Angles can be seen and measured when two rays or sides of a shape meet.

Vocabulary:

Ray - A ray is a part of a line that continues without end in one direction. It has one endpoint.

Vertex - The point at which two line segments or rays meet to form an angle.

Protractor - An instrument used to draw and measure angles.

Degree (in angles) - A unit of angle measure. The symbol for degree is °. A right angle has a measure of 90 degrees. It can be written as 90°.

Inner scale (of a protractor) - The inner set of readings on a protractor used for measuring angles.

Outer scale (of a protractor) - The outer set of readings on a protractor used for measuring angles.

Acute angle - An angle with a measure less than 90 degrees.

Obtuse angle - An angle that has a measure greater than 90 degrees.

Straight angle - An angle with a measure of 180 degrees.

Turns (and right angles) - Turns in a circle correspond to the degrees of a circle; 1/4 of a turn is 90 degrees. 1/2 of a turn is 180 degrees. 3/4 of a turn is 270 degrees. A full turn is 360 degrees.