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# FP2 De Moivre Help Watch

1. have attempted this question loads now and can't get anywhere:

by using 2cos(ntheta)=e^(intheta)+e^(-intheta) for suitable values of n, show that:
32cos^6(theta)=cos(6theta)+6cos( 4theta)+15cos(2theta)+10

have tried binomial expansion but I couldn't get anywhere, is that the right way to start?
2. Yes, it is. Picking n = 1, , then raise both sides to the six and expand. Try grouping terms of the expansion of the form and , and use what you've been given for cos(n theta).
3. Big thanks

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Updated: December 17, 2010
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