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