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Math Help - URGENT: Trig Identities Help

  1. #1
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    URGENT: Trig Identities Help

    Merci!
    Last edited by Lolcano; June 9th 2010 at 07:21 AM.
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  2. #2
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    Quote Originally Posted by Lolcano View Post
    So, I need help with this problem.


    Solve:

    cos 2 x(2 cos x+1) = 0 for 0 <= x < 360
    \cos(2x)[2\cos{x} + 1] = 0

    set each factor equal to 0 ...


    \cos(2x) = 0

    2x = 90 \, , \, 270 \, , \, 450 \, , \, 630

    x = 45 \, , \, 135 \, , \, 225 \, , \, 315


    \cos{x} = -\frac{1}{2}

    x = 120 \, , \, 240
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  3. #3
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    Quote Originally Posted by Lolcano View Post
    So, I need help with this problem.


    Solve:

    cos 2 x(2 cos x+1) = 0 for 0 <= x < 360

    Using the double angle trig identities, cos 2 x can be simplified to:
    2 cos^2 x - 1

    2 cos^2 x - 1(2 cos x + 1)
    Be careful, should be (2 \cos^2 x - 1)(2 \cos x + 1)

    Expand this a make a substitution i.e. \cos x = a and solve for a using the quadratic formula
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