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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

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    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


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    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)
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