TrigReduce

TrigReduce[expr] rewrites products and powers of trigonometric functions in terms of trigonometric functions with combined arguments.

Examples

Reduce trigonometric products:

TrigReduce[Sin[x]^2]
(* 1/2 (1 - Cos[2 x]) *)

Combine products:

TrigReduce[Sin[x] Cos[y]]
(* 1/2 (Sin[x - y] + Sin[x + y]) *)

Please visit the official Wolfram Language Reference for more details.