# Sections 2.4 Sum and Difference Formulas

**Section Objectives**

- Use sum and difference formulas to evaluate trigonometric functions.
- Use sum and difference formulas to verify trigonometric identities.
- Use sum and difference formulas to solve trigonometric equations.

### Sum and Difference Formulas

There are six common sum and difference formulas. Here they are written in compact form:

#### Examples for Objective 1

- Find the exact value of .

- Find the exact value of .

- Write as an algebraic expression.

#### Examples for Objective 2

- Use a sum formula to rewrite .

- Use a sum formula to expand .

#### Examples for Objective 3

- Find all solutions in the interval :

- Find all solutions in the interval :