1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook