
### Instruction: help me answer this question Prove that (sin 3x + sin x) sin x + (cos 3x – cos x) cos x = 0, think step by step
### Assistant: This involves the use of trigonometric formulas and simplification. , The answer is LHS = sin 3x sin x + sin^2 x + cos 3x cos x – cos^2 x = cos 2x – cos^2 x = 0 = RHS
