Chapter 9 Angles
* Angles can be seen and measured when two rays or sides of a shape meet.
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.