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Homework Help: Determine the point(s) of inflection in the equation

  1. Jul 28, 2006 #1
    I dont know if i'm posting in the wrong section, because I'm doing this intoductory calculus at high school level:

    Anyways heres my question:

    Determine the point(s) of inflection in the equation:

    y = e^x + e^-x

    I know that you have to find y'' and isolate for x to find point(s) of inflection.

    My work (sorry if its a pain to read, I dont know how to use latex)

    y=e^x + e^-x

    y' = [ (e^x)(x) ] + [ (e^-x)(-x) ]

    y'' = [ (e^x)(x)(1) ] + [ (e^-x)(-x)(-1) ]
    y'' = (e^x)(x) + (e^-x)(x)
    y'' = x(e^x + e^-x)

    I'm stuck here.
     
  2. jcsd
  3. Jul 28, 2006 #2

    HallsofIvy

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    No!! The derivative of e^x is e^x, not "(e^x)(x)". The derivative of e^(-x) is -e^(-x) not "e^(-x)(-x)".

     
  4. Jul 28, 2006 #3
    Whoops i got confused, I thought derivative of e^f(x) was [e^f(x)] x f(x)

    thanks
     
  5. Jul 28, 2006 #4

    Office_Shredder

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    it's e^f(x)*f '(x)
     
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