1. The problem statement, all variables and given/known data Use double-angle and addition formulæ and other relations for trigonometrical functions to find an expression for sin(3x) in terms of sin x alone. My problem is I don't know what is meant by "find an expression for sin(3x) in terms of sin x alone.". I know the relevant formulae but do not know what is actually wanted of the question. I know I can 'split' it by going sin(2x + x) then using addition formulae... But I don't know why or what is expected as a final answer. An equation involving only sin and no cos? 2. Relevant equations Trig identities, addition formulae 3. The attempt at a solution No idea. PS. I found the answer online but had no idea why that's the answer - please don't just give me the answer :).