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Math Help - Simplifying trig functions

  1. #1
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    Simplifying trig functions

    I'm sure that I'm missing an identity here, but how do I get from:

    -4cos(t)cos(2t)-2sin(t)sin(2t)

    to

    -4cos3(t)

    Thanks for any help.
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  2. #2
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    Re: Simplifying trig functions

    Quote Originally Posted by MajMinor View Post
    I'm sure that I'm missing an identity here, but how do I get from:

    -4cos(t)cos(2t)-2sin(t)sin(2t)

    to

    -4cos3(t)

    Thanks for any help.
    Use the product to sum identities to get

    -4\left( \frac{\cos(3t)+\cos(t)}{2} \right)-2\left( \frac{\cos(t)-\cos(3t)}{2} \right) = -\cos(3t)-3\cos(t)

    by the triple angle forumla you get the desired result

    -4\cos^3(t)
    Thanks from MajMinor
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  3. #3
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    Re: Simplifying trig functions

    Thanks for the help.
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