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Math Help - Need help solving for x

  1. #1
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    Need help solving for x

    I just started a class called advanced engineering mathmatics and I guess that includes trigonometry from highschool. If anyone could help that would be great because I haven't done this stuff in years. Here are the problems:
    Solve for x:

    18cos^2x + 3cosx - 1 = 0

    cosx + 3sinx = 1

    13^(3x) * 4^(2x) = 5

    Thanks for any help in advance, this wouldn't be a problem if the book wasn't sold out at the bookstore.
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  2. #2
    GAMMA Mathematics
    colby2152's Avatar
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    Quote Originally Posted by nafix View Post
    I just started a class called advanced engineering mathmatics and I guess that includes trigonometry from highschool. If anyone could help that would be great because I haven't done this stuff in years. Here are the problems:
    Solve for x:

    18cos^2x + 3cosx - 1 = 0

    cosx + 3sinx = 1

    13^(3x) * 4^(2x) = 5

    Thanks for any help in advance, this wouldn't be a problem if the book wasn't sold out at the bookstore.
    1) Let y=cos(x); use the quadratic equation to solve for y, and then solve for x

    2) x = 0

    3)
    13^{3x} * 4^{2x} = 5

    2197^x 16^x = 5

    (2197*16)^x = 5

    ln(2197*16)x = ln(5)

    10.47x = 1.61

    x = .154
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  3. #3
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    Much appreciated Colby.
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