### 10.2.1 Expanding a trigonometric expression

The trigexpand command expands sums, differences and products by an integer inside the trigonometric functions.

- trigexpand takes expr, an expression containing trigonometric functions.
- trigexpand(expr) returns the expression with sums, differences and integer products inside the trigonometric functions expanded.

trigexpand(cos(x+y))

cos x cos y−sin x sin y |  |  |  |  |  |  |  |  |  |