Trigonometric Sum and Difference Formulas

The sum and difference formulas for the trigometric functions sin and cosine (sometimes called the sum and difference identities) allow you to break up a single trigonometric function into a constituent of sin and cosine.

Cosine

The sum formula for cosine:

\[ cos(x + y) = cos(x)cos(y) - sin(x)sin(y) \]

The difference formula for cosine:

\[ cos(x -0 y) = cos(x)cos(y) + sin(x)sin(y) \]