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Logarithmic equation

  • Thread starter Essnov
  • Start date
  • #1
21
0

Homework Statement


I'm trying to solve this logarithmic equation, which has 3 possible solutions. However, I can only get to one of them. What are other ways I can solve it so I get to these other solutions?


Homework Equations


(ln x)^3 = 3 ln x


The Attempt at a Solution


(ln x)^3 = 3 ln x
(ln x)^2 = 3
ln x = sqrt(3)
e^sqrt(3) = x
 

Answers and Replies

  • #2
cristo
Staff Emeritus
Science Advisor
8,107
73
MAke the substitution y=lnx. Then your equation becomes y3-3y=0. Can you solve this for y?

(Note: You don't have to make the substitution; you could do it using your method. Your problems are:
(ln x)^3 = 3 ln x
(ln x)^2 = 3
Here you lost a solution by dividing by lnx
ln x = sqrt(3)
Here you only took one value of the square root)
 
Last edited:
  • #3
21
0
Thanks a lot.

x = 1, e^sqrt(3), e^-sqrt(3)
 

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