Chapter 1: Tools of

Geometry

Lesson 4: Angle Measure

Definitions

» Degree- the unit of measurement for an angle» Ray- a part of a line which has one endpoint and one end

that extends infinitely (name with the endpoint first and then any other point on the ray)

» Opposite rays- two rays that share an endpoint and extend in opposite directions (together they make a line)

» Angle- formed by two non-collinear rays that have a common endpoint

» Sides of an angle- rays» Vertex- the common endpoint of the rays of an angle» Angle Bisector- a ray or line that divides an angle into two

congruent angles

Naming and Classifying AnglesAngle:

-B is the vertex-ray BA and ray BC are the

sides( BA and BC )-Angle names:

ABC, CBA B, 4

-Angle bisector : makes 2 congruent angles

Name Measure Model

Right Angle

90

Acute Angle

Less than 90

(0 < x < 90)

Obtuse Angle

Between 90 and 180(90 < x < 180)

A

BC

4

Examples

A. Name all angles that have B as a vertex.

B. Name the sides of 5.

C.

Examples

A. Measure TYV and classify it as right, acute, or obtuse.

B. Ray YT bisects angle SYU. Angle TYS = 2x-24, angle UYT = x+16.

Find x and the measure of angle SYU.