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 need help with derivatives?

  1. Jul 6, 2006 #1
    Question is:
    Evaluate the following limits
    lim x--> 0 4^x - e^2x / 2x
    So i take derivatives
    but thats where im confused.... Whats the derivate of 4^x... x4^-x???
    and is the derivative of -e^2x -2e^x???
    So then that leaves me with 4x^-x -2e^x /2which is 0... so do i do derivatives again??? It seems like the x's wont go away????
    Last edited: Jul 6, 2006
  2. jcsd
  3. Jul 6, 2006 #2


    User Avatar
    Homework Helper

    You can use the chain rule and the fact that the derivative of e^x is e^x to answer both questions. That is, the derivative of e^f(x) is e^f(x)*f'(x). Try to rewrite 4^x as e^f(x). (use logs)
  4. Jul 7, 2006 #3

    You can take it from there.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook