How do I rewrite ln9-3ln(squareroot 3) + ln81 in the form kln3?

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Discussion Overview

The discussion revolves around rewriting the expression ln9 - 3ln(√3) + ln81 in the form kln3, where k is an exact fraction. The focus is on applying logarithmic properties and rules to manipulate the expression correctly.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant seeks help with rewriting the expression and expresses uncertainty about the process.
  • Another participant reminds about the logarithmic property ln(a^(b)) = b*ln(a) as a useful rule.
  • A participant suggests rewriting the expression as 2ln3 - 3ln(√3) + 4ln3 but is unsure how to proceed from there.
  • Further clarification is provided about taking the square root being equivalent to raising to the 1/2 power and combining logarithms before simplifying.
  • One participant proposes using the substitution √3 = 3^(1/2) to find a common factor of ln(3).
  • There is a discussion about the correct interpretation of the coefficients and denominators in the logarithmic expressions, with some confusion about the values involved.
  • Another participant corrects a misunderstanding regarding the denominator in the expression and provides a step-by-step breakdown using the sum rule of logarithms.
  • A later reply confirms understanding after reviewing the corrections and expresses gratitude for the assistance received.
  • Advice is given about keeping definitions handy when working through mathematical problems, especially those not recently practiced.

Areas of Agreement / Disagreement

Participants engage in a collaborative effort to clarify the steps needed to rewrite the expression, with some initial confusion about logarithmic properties. Corrections are made, but no consensus is reached on a final answer until the end of the discussion.

Contextual Notes

The discussion reflects a review of logarithmic properties and their application, with participants working through misunderstandings and clarifying definitions. Some assumptions about prior knowledge and familiarity with logarithmic rules are present.

Who May Find This Useful

This discussion may be useful for students reviewing logarithmic properties, particularly in the context of rewriting expressions and applying mathematical rules accurately.

phy
i need help with this one question; we have to write ln9-3ln(squareroot 3) + ln81 in the form kln3 where k is an exact fraction; i don't remember how to do this at all so any help would be greatly appreciated; thanks
 
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Remember the general rule : ln(a^(b))=b*ln(a)
 
so i could rewrite it as 2ln3-3ln(sqrt3)+4ln3; but then what?
 
Remember that taking the square root is the same as raising to the 1/2 power. You may also want to combine the logs before making the exponents into the coefficients. Do you remember your log properties?
 
um, not really
 
Use Moose352 suggestion of sqrt(3)=3^(1/2). You will now have ln(3) as a common factor.
 
so would the answer just be 4(4/3)ln3?
 
How did you get the 1/3 denominator?
 
well i said that 3ln(sqrt3) is the same as 3ln(3^1/2) which is the same as 3/2(ln3)
 
  • #10
I'm with you there, that's correct.
But it's 2 in the denominator not 3!
 
  • #11
yeah so don't we do 3*1/2 which is 3/2? i'll show you what I've done so far.
2ln3-3/2ln3+4ln3
(4ln3)(2ln3)/(3/2ln3)
4(4/3)ln3
 
  • #12
Allright, I see were you have mixed up:

Sum rule logarithm: ln(x)+ln(y)=ln(x*y)
This is not what you have done.
Exponent rule logarithms: ln(a^(b))=b*ln(a)

If you want to do it with the sum rule, write:

2ln(3)-3/2ln(3)+4ln(3)=ln(3^(2))+ln(1/(3^(3/2)))+ln(3^(4))=
ln(3^(2-3/2+4))=ln(3^(9/2))=9/2ln(3)

I'll check up on this thread tomorrow..
 
  • #13
ok i get it now; i see where i made my mistake. thanks a lot for your help :)
 
  • #14
A good advice:
When doing maths you are not too familiar with, keep the definitions right in front of you while you're working, until you don't need to look at them anymore.
 
  • #15
yeah, that is good advice; it's just that that was a review question from my calculus textbook, stuff that we learned in high school and haven't seen in some time; we were just expected to remember how to do it and i forgot; well, thanks for all your help
 

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