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Homework Help: Quick Inequality Question

  1. Mar 18, 2009 #1
    I'm working on a problem in which I have to find a range for r. I have an upper bound on it, but I can't seem to get the lower bound.

    Here is the inequality to start with:
    [tex]\lambda[/tex]r - r3 + [tex]\lambda[/tex] < 0

    Eventually, I get it down to:
    [tex]\lambda[/tex] < [tex]\frac{r^3}{r+1}[/tex]

    However, I need r by itself on one side, and I have no idea what to do. Is there anything I actually could do or am I stuck?

    Another note: r>0 and [tex]\lambda[/tex]>0. Thanks!
  2. jcsd
  3. Mar 19, 2009 #2
    You need to solve [itex]\lambda r -r^3+\lambda=0[/itex] first.
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