Find ab if log_b(a) = log_a(b)

  • Context: MHB 
  • Thread starter Thread starter My Name is Earl
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the equation log_b(a) = log_a(b) and seeks to determine the value of ab under the conditions that a and b are not equal, both are greater than zero, and neither is equal to one. The focus is on mathematical reasoning and exploration of the implications of the logarithmic relationship.

Discussion Character

  • Mathematical reasoning

Main Points Raised

  • Some participants propose letting x = log_a(b) = log_b(a), leading to the equations a^x = b and b^x = a.
  • Participants discuss the implications of dividing these equations, resulting in the expression (a/b)^x = (a/b)^-1.
  • One participant concludes that this implies ab = 1.
  • Another participant agrees with the conclusion that ab = 1.

Areas of Agreement / Disagreement

There is agreement among some participants that ab = 1 is a valid conclusion derived from the logarithmic relationship, but the discussion does not explore any alternative conclusions or unresolved points.

Contextual Notes

The discussion assumes certain conditions about the values of a and b, such as their positivity and inequality, but does not delve into potential limitations or alternative interpretations of the logarithmic properties involved.

My Name is Earl
Messages
12
Reaction score
0
I have tried various methods to solve this...

If logb(a) = loga(b) where a != b (!= means does not equal), ab > 0 and neither a nor b are 1, then what is the value of ab?
 
Mathematics news on Phys.org
My Name is Earl said:
I have tried various methods to solve this...

If logb(a) = loga(b) where a != b (!= means does not equal), ab > 0 and neither a nor b are 1, then what is the value of ab?

Let's let:

$$x=\log_a(b)=\log_b(a)$$

Now this implies:

$$a^x=b$$

$$b^x=a$$

Dividing the former by the latter, we obtain:

$$\left(\frac{a}{b}\right)^x=\left(\frac{a}{b}\right)^{-1}$$

What does this imply?
 
MarkFL said:
Let's let:

$$x=\log_a(b)=\log_b(a)$$

Now this implies:

$$a^x=b$$

$$b^x=a$$

Dividing the former by the latter, we obtain:

$$\left(\frac{a}{b}\right)^x=\left(\frac{a}{b}\right)^{-1}$$

What does this imply?

This implies that ab = 1
 
My Name is Earl said:
This implies that ab = 1

Yes, that's what I found as well. (Yes)
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 2 ·
Replies
2
Views
1K
Replies
4
Views
2K
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 18 ·
Replies
18
Views
4K
  • · Replies 14 ·
Replies
14
Views
3K
Replies
1
Views
2K