Quick Review 4-1

Unit 4 - Objective 1 - Angles

An angle is formed by two rays that have the same endpoint. This common endpoint is called the vertex of the the angle and the two rays are called the sides of the angle.

u4obj101.gif (2490 bytes)

Angles may be measured using degrees or radians. If the rotation of the terminal side from the initial side is counterclockwise, the angle is positive. If the rotation is clockwise, the angle is negative.

Examples:

If there is no degree symbol (°) after the angle measure, then assume that it is a radian measure. Each degree is divided into 60 minutes and each minute into 60 seconds. The symbol ' is used for minutes and " for seconds. So 60' = 1° and 60"=1'. In decimal degrees:

15' = (15/60)° = 0.25° and 27" = (27/3600)° = 0.0075°

Conversion between Degrees and Radians

To change from radians to degrees, multiply the number of radians by 180°/p
To change from degrees to radians, multiply by p/180°

Examples:

1 radian	=	1 (180°/p)	180°/3.1416	57.296°
				or
				57°

1°

1° (p/180°)

3.1416/180°

0.01745 radians

p/4 radians

p/4 (180°/p)

180°/4

45°

60°

60° (p/180°)

p/3 radians