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Solving for X (grph.calculator needed?)

  1. Aug 22, 2011 #1
    1. The problem statement, all variables and given/known data
    Solve For x: x3 + 2x2 - 11x = 6


    2. Relevant equations
    N/A


    3. The attempt at a solution
    I got to x3 + 2x2 - 11x - 6 = 0

    It says to list the windows I work with (using a graphing calculator). I am unable to since I don't have one and won't be assigned one until the school year starts. How do I go about solving this function for zeros.
     
  2. jcsd
  3. Aug 22, 2011 #2
    This equation doesn't factor into whole numbers. :( Using the graphing calculator, you would graph it and then use the trace tool to find the roots. I believe there is a formula for cubic equations that is kind of like the quadratic equation but more complicated, but I don't know what it is.
     
  4. Aug 22, 2011 #3

    gb7nash

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    Homework Helper

    Try the rational root theorem:

    http://en.wikipedia.org/wiki/Rational_root_theorem

    If that doesn't work and you can't use iterative methods (which probably won't give you exact roots), it's cubic formula for you.
     
  5. Aug 22, 2011 #4
    Alright thank you. Will try and report back if I can :)
     
  6. Aug 22, 2011 #5

    I like Serena

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    I'm afraid the Rational root theorem doesn't work in this case.
    And the formula for cubic equations is pretty messy:
    http://en.wikipedia.org/wiki/Cubic_function

    I'm afraid graphic calculator it is! :wink:
     
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