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Math Help - double angle identity

  1. #1
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    Exclamation double angle identity

    4sin2Xcos2X
    A) 1/2sin16X
    B) cos8X
    C) cos4X
    D)2sin4X


    determine whether the equation is an identity. if an identity prove it.

    (sinx+cosx)^2=1

    find all solutions in [0,2pi)
    tanxsecx=squareroot of 2.

    2sinxcosx+cosx=0


    thank you so much in advanced!!!!!
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  2. #2
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    Joined
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    Quote Originally Posted by amanda0603 View Post
    4sin2Xcos2X
    A) 1/2sin16X
    B) cos8X
    C) cos4X
    D)2sin4X
    use \sin 2x = 2\sin x \cos x

    determine whether the equation is an identity. if an identity prove it.

    (sinx+cosx)^2=1
    Expand this and compare with \sin^2 x + \cos^2 x = 1, what can you deduce?

    find all solutions in [0,2pi)
    tanxsecx=squareroot of 2.
    Try using \tan x = \frac{\sin x}{\cos x} and \sec x = \frac{1}{\cos x}

    2sinxcosx+cosx=0


    thank you so much in advanced!!!!!
    Pull out a \cos x and solve each part individually (set them equal to zero)

    Good luck
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