Why Am I Getting Incorrect Solutions to This Logarithmic Substitution Problem?

  • Thread starter Thread starter brandon1
  • Start date Start date
  • Tags Tags
    Log Substitution
Click For Summary
SUMMARY

The discussion focuses on solving a logarithmic substitution problem involving the equation (\log x)^3 = \log(x). The key error identified is the incorrect manipulation of logarithmic properties, specifically the misunderstanding that (\log x)^3 does not equal \log(x^3). The correct approach involves substituting y = log x, leading to a cubic equation that yields three solutions. The solutions are x_1 = 1, x_2 = y, and x_3 = 1/y, contingent on the base of the logarithm.

PREREQUISITES
  • Understanding of logarithmic properties and identities
  • Familiarity with cubic equations and their solutions
  • Basic algebraic manipulation skills
  • Knowledge of substitution methods in algebra
NEXT STEPS
  • Study the properties of logarithms in depth
  • Learn how to solve cubic equations systematically
  • Explore substitution techniques in algebraic problem-solving
  • Review common mistakes in manipulating logarithmic expressions
USEFUL FOR

Students tackling logarithmic equations, educators teaching algebra, and anyone seeking to improve their problem-solving skills in mathematics.

brandon1
Messages
34
Reaction score
0
Physics news on Phys.org
note:
(\log x)^3 \neq \log (x^3) ie. 2nd step is wrong

hint: a make substitution: y = log x and solve for y first then x.
 
The first thing you've done is to cube both sides. That's ok but it should give you
( log(x) )^3 = log(x)
Since the whole log(x) is cubed, you can't move the 3 down (that's only if the x was cubed).

But what you can do is take all the terms over to one side and then you just have to solve a cubic (which will give you 3 solutions). You may want to make it easier to see by introducing a new variable, u = log(x) for example.
 
Good to go!
 
and the solutiions should probbably be, couse i just glanced at it,:
x_1=1
x_2=y,(if the base of the logarithm is y, couse i could not see it clear)
x_3=1/y
 
Last edited:

Similar threads

  • · Replies 12 ·
Replies
12
Views
2K
Replies
16
Views
3K
Replies
2
Views
2K
Replies
15
Views
4K
  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
6K
Replies
2
Views
2K