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    dgperk1981's Avatar
    dgperk1981 Posts: 1, Reputation: 1
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    #1

    Nov 18, 2007, 04:13 PM
    Verifying Double Angle Trig Identities
    Prove:

    cos(4x) = 1 - 8(sinx)^2(cosx)^2

    I have tried and tried and keep ending up with:

    (cosx)^4 - 6(cosx)^2(sinx)^2 + (sinx)^4
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    Nov 20, 2007, 06:04 PM
    Here's a hint:



    Use the identities:
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