1. Angles

by M. Bourne

An angle is a measure of the amount of rotation between two line segments. The 2 line segments (or rays) are named the initial sideand terminal side as shown in the diagram.

If the rotation is anti-clockwise, the angle is positive. Clockwise rotation gives a negative angle (by convention).

Examples

Gradians

There is another unit for measuring angles, called gradians. In this system, the right angle is divided into 100 gradians. Gradians are used by surveyors, but not commonly used in mathematics. However, you will see a "grad" mode on most calculators.

Anti-clockwise, positive angle.

Clockwise, negative angle.

Angles are commonly measured in degrees or radians. If you can't wait to learn about radians, see section 7. Radians.