An identity is an equation that is true for all of the possible values of its variables. Trig identities are important, they involve the sums or differences of angles.

### What are the Trigonometric Identities?

The identities in the attached image can be used to determine that other trigonometric equations are also identities. To do so, you will need to use your algebraic background to show that the expression on one side of the equals sign can be changed into the expression on the other side of the equals sign.

See also 'Trig Formula'

### Recommended Resources

**Trigonometry (Cliff's Quick Review)** If you require some additional review to assist you to grasp trigonometric identities and their applications, this resource will amply supply you with the tools you need to reinforce trigonometric concepts.All the concise and easy to follow tutorials in this selection will assist the struggling trig. student to understand identities, functions, polar coordinates, triangles, vectors and inverse functions and equations. Cliffs notes tend to be the favored among students needing some additional work in introductory levels.

**Schaum's Outline of Trigonometry** Chapter 8 deals with the trigonometric basic relationships and identities. Overall, this resource focuses on all concepts related to Plane Trigonometry. Detailed explanations, step by step solutions make this trigonometry resource one of the best to assist you to solve all types of trigonometric problems.

Whether you're looking to brush up on concepts before taking your tests or if you simply want to try to solve a variety of problems, this book is book is sure to help you understand and extend your knowledge in trigonometry.