
### Instruction: help me answer this question Prove that sin (n + 1)x sin (n + 2)x + cos (n + 1)x cos (n + 2)x = cos x, think step by step
### Assistant: N/A , The answer is sin (n + 1)x sin (n + 2)x + cos (n + 1)x cos (n + 2)x = cos x
