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Math Help - Proving Trigonometry Identities Help

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    Proving Trigonometry Identities Help

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    Last edited by fayeorwhatsoever; January 27th 2010 at 04:17 AM.
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    And also, I'm confused about this.. is -tanx-tanx equal to -2tanx or -tan2x?
    This question shows you are not familiar with the subject. My advice is that you should read your textbook/notes again. Work out few simple problems.

    By the way -tan x -tan x = -2 tan x

    I will answer your question, but I doubt you will understand every step clearly. First read the identities and know them clearly and then re read my post, you will understand the solution.

    Quote Originally Posted by fayeorwhatsoever View Post
    Prove: sin squared 2x cos squared 2x=1/8 (1-cos8x)
    \sin ^2 2x \cos^2 2x = \frac{\sin^2 4x}{4} = \frac14\left(\frac{1 - \cos 8x}{2}\right) =  \frac18 (1 - \cos 8x)

    For the first equality, I have used the relation \sin 2y = 2 \sin y \cos y

    For the second equality I have used \cos 2y = 1 - 2\sin^2 y
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