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: L'hopitals rule?

  1. Jan 24, 2009 #1
    1. The problem statement, all variables and given/known data

    Find the limit of f(x)=[xcosx]/[x^3 + 1] as x tends to infinity.

    2. Relevant equations

    3. The attempt at a solution

    Can i use l'hopitals rule here? Or if not, what are the conditions for f(x) to meet so that i may use l'hopitals rule?

    Without using l'hop i know that cosx would oscillate between -1 and 1 and that is multiplied by infinity. Then the denominator would tend towards infinity. So what is infinity over infinity?
  2. jcsd
  3. Jan 24, 2009 #2


    User Avatar
    Gold Member

    I think that you don't need L'hopital here.
    i.e, if we write it as:
    as x appraoches infinity, can you see why?
  4. Jan 24, 2009 #3
    yea, thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook