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

    Apr 24, 2013, 11:01 PM
    verify the identity
    (cos3x + sin3x)/(cos3x - sin3x) - (cos3x - sin3x)/(cos3x + sin3x) = 2tan6x

    help please. I'm lost. I substitute w for 3x then go from there but I get stuck at 4sinwcosw/(2cos^2w-1)
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Apr 25, 2013, 05:57 AM
    Quote Originally Posted by nohea
    i get stuck at 4sinwcosw/(2cos^2w-1)
    2sinwcosw/(cos^2w-sin^2w) is the formula for tan(2w):

    tan(2w) = sin(2w)/cos(2w) = 2 sin(w)cos(w)/(2cos(w)-1)

    So you're there!
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