# 5: Trigonometric Functions


The trigonometric functions are functions of an angle. and relate the angles of a triangle to the lengths of its sides. They are important in the study of triangles and modeling periodic phenomena, among many other applications.

• 5.1: Angles
How to draw angles in standard position. Positive and negative angles measured in degrees and in radians. Conversion between degree and radian measure. Finding coterminal angles.
• 5.2: Right Triangle Trigonometry
Trigonometric functions are defined for right triangles. Find all trigonometric ratios given 3 sides or given 1 trigonometric ratio. Solve for all sides and angles given 2 sides or given one side and one angle. Examples of right triangle applications are given. Find an acute angle given 2 sides and related applications. Cofunction identities. Most examples in this section use degrees.
• 5.3: Sine and Cosine Functions
In this section, we will examine this type of revolving motion around a circle. To do so, we need to define the type of circle first, and then place that circle on a coordinate system. Then we can discuss circular motion in terms of the coordinate pairs.
• 5.4: The Other Trigonometric Functions
Trigonometric functions allow us to specify the shapes and proportions of objects independent of exact dimensions. We have already defined the sine and cosine functions of an angle. Though sine and cosine are the trigonometric functions most often used, there are four others. Together they make up the set of six trigonometric functions. In this section, we will investigate the remaining functions.

## Contributors

5: Trigonometric Functions is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.