Solving Logarithmic Equation: Why Isn't It Working?

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Homework Help Overview

The discussion revolves around solving a logarithmic equation involving different bases, specifically the equation log_2 x + log_4 x = 2. Participants are exploring the application of the change of base rule and the implications of converting logarithms to a common base.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the validity of using the change of base rule and question the steps taken to combine logarithmic terms. There is confusion regarding the transition to a common base and the simplification of terms.

Discussion Status

Some participants have provided insights into the simplification process, noting that combining logarithms into a single base can clarify the solution. However, there remains some uncertainty about specific steps and the reasoning behind certain transformations.

Contextual Notes

Participants express concerns about potential mistakes in their calculations and the interpretation of logarithmic properties. There is an ongoing exploration of how to manipulate logarithmic expressions correctly without losing track of the original equation.

tweety1234
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Homework Statement



I can't seem to get my head round this problem, I know how to use the 'change the base rule'

log_2 x + log_4x = 2

\frac{logx}{log2} + \frac{logx}{log4} = 2

why is this not correct ??
 
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It looks correct - what's the problem
(of course everytime I stray into maths I make an dumb mistake!)
 
mgb_phys said:
It looks correct - what's the problem
(of course everytime I stray into maths I make an dumb mistake!)

well the answer book gives the solution like this,

log_2x + \frac{log_2 x}{log_2 4} = 2 don't understand why its base 2 here?

log_2 x + \frac{log_2 x}{2} =2

\frac{3}{2}log_2 x = 2 don't understand were 3/2 came from ?

log_2 x = \frac{4}{3}

x = 2^{\frac{4}{3} }
 
They are just collapsing it all into the same base log.

log_2 x + \frac{log_2 x}{2} =2 is just

1.5 * log_2 x =2 which is

\frac{3}{2} * log_2 x =2

It's the same answer as you get - but you can do it this way without needing to calculate log() of anything
 
tweety1234 said:
log_2 x + log_4x = 2

\frac{logx}{log2} + \frac{logx}{log4} = 2

so is this method still correct? can I just add both logs up ?
 
Except you are trying to find X so first you have to multiply out log(2) and log(4)
 
mgb_phys said:
They are just collapsing it all into the same base log.


log_2 x + \frac{log_2 x}{2} =2 is just

1.5 * log_2 x =2 which is

\frac{3}{2} * log_2 x =2

It's the same answer as you get - but you can do it this way without needing to calculate log() of anything

sorry, I still don't get where 1.5 comes from ? I thought you just multiply both sides by two to get rid of the fraction ?

2log_2 x + log_2 x = 4
 
log_2 x + \frac{log_2 x}{2} = 2

Which if you ignore the logs for now is just; a + a/2 = 2

a(1+1/2) = 2

1.5a = 2

3/2 a =2
 
mgb_phys said:
They are just collapsing it all into the same base log.

log_2 x + \frac{log_2 x}{2} =2 is just

1.5 * log_2 x =2 which is

\frac{3}{2} * log_2 x =2

It's the same answer as you get - but you can do it this way without needing to calculate log() of anything

mgb_phys said:
log_2 x + \frac{log_2 x}{2} = 2

Which if you ignore the logs for now is just; a + a/2 = 2

a(1+1/2) = 2

1.5a = 2

3/2 a =2

oh I get it now, thanks a lot for your help!
 

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