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: About l'hopital rule

  1. Nov 29, 2007 #1
    [SOLVED] About l'hopital rule

    I have two solutions for a question about limit
    http://tinyurl.com/2pknkb

    May I know is (a) correct, or (b)?
    What is the reason for the other to be wrong?

    Note:
    (a) just directly applies l'hopital rule to numerator
    (b) is to reduce the numerator using logarithm formula before using l'hopital rule
     
  2. jcsd
  3. Nov 29, 2007 #2

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    You didn't calculate the derivative correctly for (b). You need to apply the chain rule. If you had computed it correctly you would have arrived at the same answer as for (a).

    [tex]\frac d{dx}(\ln(x+1)-\ln(2)) = \frac d {dx} \ln\left(\frac{x+1} 2\right) = \frac 2 {x+1} \; \frac d {dx}\frac {x+1} 2 = \frac 2 {x+1} \, \frac 1 2 = \frac 1 {x+1}[/tex]
     
  4. Nov 29, 2007 #3
    I see, thank you very much!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook