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Math Help - multiplying trig functions

  1. #1
    Newbie
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    Feb 2008
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    multiplying trig functions

    could you help me on the following,

    rcosxcosy * rsinxcosy

    -rsinxsiny * sinxsiny
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  2. #2
    Senior Member
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    Dec 2007
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    Anchorage, AK
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    r\cos{x}\cos{y}\cdot{r}\sin{x}\cos{y}=r^2\sin{x}\c  os{x}\cos^2{y}
    -r\sin{x}\sin{y}\cdot\sin{x}\sin{y}=-r\sin^2{x}\sin^2{y}

    -Kevin C.
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  3. #3
    Newbie
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    cheers mate.

    now could you possibly help me simplify the following plz,

    cosx[(r^2sinxcos^2y) - (r^2sinxcosxsin^2y)]

    (-rsinx)[(rsin^2xcos^2y) - (-rsin^2xsin^2y)]

    I'm sorry i'm askin for help, i kno this must be easy, but i can't do it. lol
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  4. #4
    Senior Member Peritus's Avatar
    Joined
    Nov 2007
    Posts
    397
    try using the following identities:

    <br />
\begin{gathered}<br />
  \cos ^2 x - \sin ^2 x = \cos 2x \hfill \\<br />
  2\sin x\cos x = \sin 2x \hfill \\<br />
  \sin ^2 x + \cos ^2 x = 1 \hfill \\ <br />
\end{gathered} <br />

    you might also take a look at this:

    Table of Trigonometric Identities
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