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Quick(ish) homework help

  1. Sep 11, 2009 #1
    Need to solve the following equation for x

    x^3 + (2x10^5)x^2 + 250x - (5.08x10^-3) = 0

    I've tried factoring, and quickly found the quadratic formula to be a dead end. Answer has to be a real number. I just need to know how to do it, not necessarily the answer. Thanks all!
  2. jcsd
  3. Sep 12, 2009 #2
  4. Sep 12, 2009 #3


    Staff: Mentor

    Inasmuch as your equation is a cubic (third-degree polynomial), the quadratic formula doesn't apply. It can be used only on quadratic (second-degree) equations. IOW, equations of the form ax2 + bx + c = 0
    There is a formula that can be used to solve cubic equations, that was developed sometime in the 14th century or so by an Italian mathematician. I don't remember the name of the algorithm, but if you searched Wikipedia you might be able to find it.
  5. Sep 12, 2009 #4


    User Avatar
    Science Advisor
    Homework Helper

    Use a numerical method to find the root, please? The root is very likely not rational and the analytic method will paralyze you with complications, all grace to Cardano. Try bisection first. You can do it on a calculator.
    Last edited: Sep 12, 2009
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