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: What am I doing wrong in this derivative

  1. Mar 11, 2014 #1
    my derivative of log4(r)*log2(r)= log2(r)/rln(4)+log4(r)/rln(2)

    my book says the derivative should be 2(ln(r))/(r(ln(2))(ln(4))
    what am I doing wrong?
  2. jcsd
  3. Mar 11, 2014 #2
    Do you know how to convert logs to different bases?
  4. Mar 11, 2014 #3

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    What does log4(r) mean? Is it ##\log(4r)##, log to base 4 of r, or is it ##\log(r)^4##?
  5. Mar 11, 2014 #4


    User Avatar
    Homework Helper

    You can simplify your expression further:
    \frac{\log_2(r)}{r \ln 4} + \frac{\log_4(r)}{r \ln 2} =
    \frac{\ln r}{(r \ln 4) \ln 2} + \frac{\ln r}{(r \ln 2) \ln 4}
    = \frac{2 \ln r}{r \ln 2 \ln 4}
  6. Mar 11, 2014 #5
    1/ln(b)*1/r* dy/dx(r)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted