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Simple equation solving (I think)

  1. Dec 19, 2008 #1
    1. The problem statement, all variables and given/known data

    Find x-intercepts of f(x)= ln(x+1)-(sinx)^2

    I know to get to ln(x+1)=(sinx)^2 but have no idea what to do after that.
  2. jcsd
  3. Dec 19, 2008 #2
    I don't think it's THAT easy, x = 0 comes to mind though
  4. Dec 19, 2008 #3


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    It turns out that there are 3 x-intercepts (x=0 is the obvious one). You can estimate what domain they lie in by looking at the maximum and minimum values of [itex]\sin^2(x)[/itex]...what are those? What does that tell you about the max/min of [itex]\ln(1+x)[/itex] for which there might be any x-intercepts? You can use that to determine a range of x-values for which x-intercepts are possible.

    The next step would be to graph [itex]f(x)[/itex] over that Domain and estimate value for the x-intercepts.

    If you are familiar with Newton's method, you can improve your estimations through a few iterative calculations.
  5. Dec 19, 2008 #4
    This seems to be kind of an overkill for someone in pre-calc though unless you were allowed to use a CAS.
  6. Dec 22, 2008 #5
    Use iteration?
  7. Dec 22, 2008 #6
    Yes you could use Newton's as was mentioned but I still maintain it's a somewhat hard problem for pre-calc then again I never took pre-calc and maintain that it's a useless class :)
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