It's easy to see that is n is an odd positive integer, and if n is an even positive integer, But how would you prove that?
Last edited by Random Variable; Feb 23rd 2010 at 10:12 PM.
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By induction ? Or else, use what you know about odd numbers : if n is even, n=(n-1)+1, where (n-1) is odd. and use the addition formula for the sine function.
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