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and hence for sin(3a) write
Now expand sin(2a) and use the expression for cos(p + q) to expand cos(2a). Simplify the final expression to get the form you want. I hope this helps, Hi mailene, I'll give you a strategy for the first one, and then see if you can figure out the others, since they are similar. Required to prove: sin(3a)=3sin(a)4sin^3(a) Strategy: Following this, apply double angle formulae. For cos(2a) remember that you are trying to get a final expression in terms of sin(a), so choose the appropriate double angle formula. sin(2a) = 2sin(a)cos(a) You may also need to use the identity cos^{2}(a) + sin^{2}(a) = 1 to get everything in terms of sin(a). Hope this helps,  


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