Establish the following identity: Our hint is to use DeMoivre's formula, I have no idea where to begin and any help would be appreciated!
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Originally Posted by Chief65 Establish the following identity: Our hint is to use DeMoivre's formula, I have no idea where to begin and any help would be appreciated! . Now let .
A shorter method: Using De Moivre's Theorem Using binomial expansion: Equating the real parts: Substituting as required
Last edited by Gusbob; Dec 12th 2009 at 06:12 PM. Reason: Stupid mistake
Originally Posted by Gusbob A shorter method: Using De Moivre's Theorem Using binomial expansion: Equating the real parts: Substituting as required That's probably the preferred method, as I'm sure the next part of the question is to prove the triple/third-angle identity for sine, which I already used in my proof...
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