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    stateline's Avatar
    stateline Posts: 2, Reputation: 1
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    #1

    Oct 27, 2007, 09:06 PM
    trigonometric identities
    find an equivalent expression for cos^4 x in terms of function values of x, 2x, or 4x, raised only to the first power
    terryg752's Avatar
    terryg752 Posts: 197, Reputation: 4
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    #2

    Oct 27, 2007, 11:40 PM
    You should use the following:

    1 + cos 2x = 2 cos^2 x

    Hence Cos^2 x = (1 + cos 2x)/2

    NB Two very useful formulae for such problems :

    1 + Cos 2x = 2 Cos^2 x

    1 - Cos 2x = 2 Sin^2 x
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