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Math Help - trig

  1. #1
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    trig

    verify the identity: cos5t-cos3t= -8sin(squared)t[(2cos(cubed)t-cost)]
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  2. #2
    Moo
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    Hello,

    cos(5t)=cos(4t+t)=cos(4t)cos(t)-sin(4t)sin(t)

    cos(4t)=cos(2*2t)=2cos²(2t)-1
    sin(4t)=sin(2*2t)=2cos(2t)sin(2t)

    Continue and finish it...

    There had to be a relation that can simplify, but i can't get on it anymore...
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