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Math Help - Need a hand on this problem

  1. #1
    Newbie BeachLover's Avatar
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    Need a hand on this problem

    Hello all,
    I am new to this forum as my post counter will show, and I have a toughy right out of the box. Can someone please point me in the right direction?
    I am a little fuzzy on this as I have not been in school for 20 years.
    Goes to show how much we use this junk huh?

    DeMoivre’s Theorem states, “If z = r(cos u + i sin u), then zn = rn(cos nu + i sin nu).”

    I have to verify for n=2. Where the heck am I supposed to start?
    I do not remember DeMoivre's Theorem.
    Any help would be greatly appreciated.
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  2. #2
    MHF Contributor

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    \begin{array}{rcl}<br />
   {\left[ {\cos (t) + i\sin (t)} \right]^2 } &  =  & {\left( {\cos ^2 (t) - \sin ^2 (t)} \right) + i\left( {2\cos (t)\sin (t)} \right)}  \\<br />
   {} &  =  & {\cos (2t) + i\sin (2t)}  \\<br /> <br />
 \end{array}
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