Expanding a trigonometric expression: trigexpand

### 6.23.1 Expanding a trigonometric expression: trigexpand

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

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

Input:

trigexpand(cos(x+y))

Output:

cosx· cosy−sinx· siny