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Math Help - Prove the identity

  1. #1
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    Prove the identity

    This is another problem which I am not able to complete

    Prove the following identity.

    sin(4x) = 8sin(x)cos^3(x)-4sin(x)cos(x)
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  2. #2
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    Re: Prove the identity

    Quote Originally Posted by MathRaven View Post
    This is another problem which I am not able to complete
    Prove the following identity.
    sin(4x) = 8sin(x)cos^3(x)-4sin(x)cos(x)
    \sin(4x)=2\sin(2x)\cos(2x)=2[2\sin(x)\cos(x)][2\cos^2(x)-1]
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  3. #3
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    Re: Prove the identity

    is that showing all the steps which you took?
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  4. #4
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    Re: Prove the identity

    Quote Originally Posted by MathRaven View Post
    is that showing all the steps which you took?
    it's your turn, how did he get from the 1st to the 2nd step? ... and from the 2nd to the 3rd?
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