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February 29th, 2012, 12:36 AM   #1
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De Moivre's Theorem

how to find the exact value sin??2?/5? using Demoivers Theorem algebraically ?
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February 29th, 2012, 01:31 AM   #2
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Re: De Moivre's Theorem

We may then consider the roots of the equation:

Now simply choose the complex root a + bi where a and b are positive, i.e., in the first quadrant of the complex plane. This will come from the quadratic factor whose coefficient of the linear term is negative:

and choosing the root we find:


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