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Math Help - Solve for X:

  1. #1
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    Solve for X:

    Solve for X:


    3cos(x) + 3 = -2cos^2(x), for x E [-pi, 3pi]
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  2. #2
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    Quote Originally Posted by Mr_Green View Post
    Solve for X:


    3cos(x) + 3 = -2cos^2(x), for x E [-pi, 3pi]
    2cos^2(x) + 3cos(x) + 3 = 0

    It might be easier for you to define y = cos(x), then look at:

    2y^2 + 3y + 3 = 0

    You can use the quadratic equation to solve this, discard any solutions that are greater than 1 or less than -1, then take the inverse cosine.

    The problem is that this quadratic has no real solutions. Thus you have no real solutions for x. Is there a typo perhaps?

    -Dan
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  3. #3
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    I screwed Up

    I screwed UP!
    it should be


    3cos(x) + 3 = 2 - 2cos^2(x), for x E [-pi, 3pi]


    help is apreciated!
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  4. #4
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    Use the same substitution. u=\cos(x) You'll get a quadratic.
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