Calculus - Logarithms

Discussion in 'Homework Help' started by MohtasaUnique, Jan 9, 2011.

Calculus - Logarithms
  1. Unread #1 - Jan 9, 2011 at 6:28 PM
  2. MohtasaUnique
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    Calculus - Logarithms

    So I just started my calc college course this semester, and I'm already lost because I missed a day of lecture (dentist)

    The unit we're in is logarithms and I know how to do all the basic stuff like go from logs to exponents and back again, and simplifying log equations and all that, but I don't know how to solve for x on more complex log equations.

    So an example of where I'm stuck is this:

    3^(x-1) = 2^(2x-1)

    It's probably something simple that I'm not getting, but this is how far I can go before getting stuck:

    3^(x-1) = 2^(2x-1)
    log3^(x-1) = log2^(2x-1)
    (x-1)log3 = (2x-1)log2

    And I don't know where to go from there. The answer in the book is
    x = (log3 - log2)/(log3 - 2log2)
    But it doesn't show how to get there. I'm sooooooo confused and the test is tuesday :[
     
  3. Unread #2 - Jan 9, 2011 at 7:26 PM
  4. Rsaccounttrader
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    Calculus - Logarithms

    (x-1)log3=2x-1)log2
    log3/log2=2x-1/x-1
    Do log3/log2 on calc (lets say for now it equals ANS)
    then
    ANS=2x-1/x-1
    ANSx-ANS=2x-1
    ANSx-ANS+1=2x
    1-ANS=2x-ANSx
    1-ANS=x(2-ANS)
    x=(1-ANS)/(2-ANS)
     
  5. Unread #3 - Jan 10, 2011 at 10:34 PM
  6. MohtasaUnique
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    Calculus - Logarithms

    Alright, time for another equation: Logₓ1/8 = -1/3. The back of the book says x = 512, and every working online calculator says the same, but I can't get the result.

    So far I've got:
    Loxₓ1/8 = -1/3 --> X^(-1/3) = 1/8

    But I'm lost as to what to do next.
     
  7. Unread #4 - Jan 12, 2011 at 10:13 PM
  8. The Fat Controller
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    Calculus - Logarithms

    (x^(-1/3))^3 = (1/8)^3 (cube both sides)
    x^-1 = 1/x = 1/512
    x = 512 (flip the fractions)
     
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