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Thread: Proof question

  1. November 5th 2008, 02:41 PM #1
    ctt
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    Proof question

    How can I prove 4(sin^4 x+ cos^4 x) always equals cos 4x + 3?

    I don't think I've been taught the identities that I need...

    Thanks in advance
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  2. November 5th 2008, 04:31 PM #2
    Mathstud28
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    Quote Originally Posted by ctt View Post
    How can I prove 4(sin^4 x+ cos^4 x) always equals cos 4x + 3?

    I don't think I've been taught the identities that I need...

    Thanks in advance
    Yeah, maybe not, its ugly but this one is most directly solved with

    \cos(x)=\frac{e^{ix}+e^{-ix}}{2}

    and

    \sin(x)=\frac{e^{ix}-e^{-ix}}{2i}
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