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Find Antiderivatives

  1. Dec 4, 2016 #1
    • Member warned that an effort must be shown
    1. The problem statement, all variables and given/known data

    find the anti-derivative of xe ^x so its x to the power of e to the power of x
    2. Relevant equations


    3. The attempt at a solution
    i have 0 idea where to even start. this was a question on my quiz today
     
  2. jcsd
  3. Dec 4, 2016 #2

    BvU

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    Hi dfk,

    No homework. Still an attempt on your part required :biggrin: $$ F'(x) = x^{e^x} \ \Rightarrow \ F(x) = ??$$
     
  4. Dec 4, 2016 #3
    well i know that the derivative of ex is ex so the anti derivative of ex is ex and then my attempt would be exx but i dont know if thats right or even a good start
     
  5. Dec 4, 2016 #4
    actually scratch the last part. my attempt would be xe^x +1 becacuse normally for any function x u go x and add one to the power and divide by it
     
  6. Dec 4, 2016 #5

    Mark44

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    So is ##\frac d{dx}(x^{e^x + 1}) = x^{e^x}##?

    For a power function, such as ##x^n##, the derivative is ##nx^{n - 1}##, but is that what you have here?
     
  7. Dec 4, 2016 #6

    epenguin

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    Do you confirm that the formula in #2 is the one you meant?

    Then you don't need to ask us whether a proposed solution is correct, surely you can differentiate?

    If then you find it wrong, It may at least suggest something else to try. Or maybe some other direction to look.
     
  8. Dec 4, 2016 #7
    i dont know what ur asking, the question is find the antiderivative of the function x to the power of e to the power of x as stated at the start. im not asking whether or not a solution is correct im asking how abouts would i go to try and get the antiderivative because ive tried multiple ways (one which i have stated in a different reply) and cant seem to get there. im only asking for guidance not for an answer of whether or not my solution is correct.
     
  9. Dec 4, 2016 #8
    what i meant was that it was my attempt at finding the antiderivative of xex. i know that the derivative of ex is ex therefor the anti derivative would be the same. so then for derivatives with base x you go xn-1 times the derivative of the power but since i need the anti derivative wouldnt i do xn+1 divided by the power instead? so wouldnt it be xe^x +1 all divided by ex(the plus one is added to ex not to the entire function im just having trouble showing it up on here properly)
     
  10. Dec 4, 2016 #9

    Mark44

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    That's not how it works -- you are applying the power rule for a function for which it doesn't apply.
    Power rule: ##\frac d{dx} x^n = nx^{n - 1}##
    Here the exponent, n, is a constant. For your function the exponent, ##e^x + 1## is not a constant.

    By your reasoning, ##\frac d{dx} x^x =xx^{x - 1} = x^x##, which isn't true. The derivative of ##x^x## is actually ##x^x(\ln x + 1)##.
     
  11. Dec 5, 2016 #10

    Ray Vickson

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    To get the derivative, write ##x^{e^x}= e^{f(x)}##, where ##f(x) = \ln(x) e^x##, and use the chain rule.
     
  12. Dec 5, 2016 #11

    epenguin

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    I thought and rereading #3 it still looks to me you were asking whether an answer was correct. We do often get to ask that question for integrals and have to point out that checking is the easy part - and also necessary. It seems to me you have now got some guidance to work on.
     
  13. Dec 5, 2016 #12
    ya but the question is asking for antiderivative
     
  14. Dec 5, 2016 #13

    Mark44

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    You claimed earlier that the antiderivative was ##x^{e^x + 1}##. If this is correct, you should be able to differentiate this function to get your original integrand. That's what we're helping you with.

    On the other hand, if you differentiate ##x^{e^x + 1}##, and DON'T get ##x^{e^x}##, then that tells you that your purported antiderivative is incorrect.
     
  15. Dec 5, 2016 #14
    ohh okay that makes more sense. and i wasnt claiming that thats what the antiderivative was. i was saying that was how i was trying to solve the antiderviative but was getting the wrong answer so i needed guidance to go abouts finding the antiderivative correctly. you asked what my initial attempt was which is why i responded with that, i know its wrong but u wanted to know what i did so thats why i showed that
     
  16. Dec 5, 2016 #15

    Mark44

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    In post #4 you said:
    It looks to me like you were claiming that ##x^{e^x + 1}## is the antiderivative of ##x^{e^x}##.

    Please don't use "text speak" here at PF. In the rules for this site (https://www.physicsforums.com/threads/physics-forums-global-guidelines.414380/ ), under General Posting Guidelines, it says"
     
  17. Dec 5, 2016 #16
    i said my "attempt" i never claimed anything?? but anyway nevermind i'll figure it out on my own i just wanted some help and guidance not an argument or a forum of whose wrong whose right i'll delete this shortly
     
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