equal to a straight angle, they are called supplementary angles. In Figure 3-6, angle AOB is a straight

angle, and angles AOC and BOC are supplementary angles. Angle AOC is the supplement of BOC, and

angle BOC is the supplement of AOC. When two lines intersect, the opposite angles are called vertical

angles. In Figure 3-7, angles AOD and BOC are vertical angles, and angles AOC and BOD are also

vertical angles.

Figure 3-5. Complimentary angles

Figure 3-6. Supplementary angles

Figure 3-7. Vertical angles

Degrees (€) are used for angle measurements. An angular degree is 1/360th of a circle. The degree is

further divided into minutes (') and seconds ("), with 60 minutes in 1 and 60 seconds in 1 minute.

line OP in a counterclockwise direction about point O, starting from line AO. By this action the angle

AOP is generated. When line OP is at one-quarter of a revolution, it is perpendicular to line AO, and a

right angle is formed. When you rotate line OP completely around the circle, it generates four right

angles (360). Thus, the total angular magnitude about a point in a place is equal to four right angles.