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.