1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    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!

Homework Help: 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


    User Avatar
    Homework Helper
    Gold Member

    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 :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook