How do you prove a^{x}=e^{xlna}?

  • Context: Undergrad 
  • Thread starter Thread starter Lipi
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around understanding the equivalence of the expressions \( a^{x} \) and \( e^{x \ln a} \). Participants explore the mathematical reasoning behind this relationship, particularly in the context of logarithms and exponential functions.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant seeks to understand how to prove that \( a^{x} = e^{x \ln a} \), using the example \( 10^{x} = e^{x \ln 10} \).
  • Another participant suggests taking logarithms of both sides to explore the relationship further.
  • A participant expresses confusion about the logarithmic transformation and questions how to derive \( y = e^{x \ln a} \) from \( y = a^{x} \).
  • There is a mention of the rule \( e^{\ln a} = a \) as a key insight in understanding the equivalence.
  • One participant emphasizes the definition of the natural logarithm as the inverse function of the exponential function, asserting that this underpins the relationship \( e^{\ln a} = a \).
  • Another participant elaborates on the definition of the natural logarithm and its connection to integrals, suggesting that understanding logarithmic properties is foundational to grasping the concept of Euler's number.

Areas of Agreement / Disagreement

Participants generally agree on the equivalence of the expressions involving exponentials and logarithms, but there is some confusion and lack of clarity regarding the steps to derive this relationship. The discussion remains exploratory without a definitive resolution on all points raised.

Contextual Notes

Some participants express uncertainty about the logarithmic transformations and the implications of definitions related to logarithms and exponentials. There are references to different ways of defining logarithms that may affect understanding.

Lipi
Messages
3
Reaction score
0
It's not a homework, I just want to understand the e. Just don't know enough yet to grasp it.
Can someone help me prove that this is eaqual:

a^{x}=e^{xlna}

for example

10^{x}=e^{xln10}

How do you come from 10^{x} to e^{xln10}

Thanx.
 
Physics news on Phys.org
Take logarithms of both sides of the equation, and see what you get.
 
You get zero on both sides, that's all fine. I already know it's the same.

But if you have a function y=a^{x},

how do you get to y=e^{xlna} being the same thing?
 
Lipi said:
You get zero on both sides...
I don't know what you mean. How come, zero? What is the logarithm of a^x ? And of e^(x ln a) ?
 
Oh i just got it.:shy:

Just found the rule e^{lna}=a.

Thanx for the kick in the right direction, i appreciate it:smile:
 
Do you understand WHY eln a= a? Quite simply because "ln x" is DEFINED as the inverse function to ex! That should have been one of the first things you learned about logarithms.


(And, just to shortcut possible objections, yes, it is quite possible to define ln(x)= \int_1^x 1/t dt and then define y= ex to be the inverse of THAT function. But still, because they are inverse function eln a= a and ln(ea)= a.
 
HallsofIvy said:
(And, just to shortcut possible objections, yes, it is quite possible to define ln(x)= \int_1^x 1/t dt and then define y= ex to be the inverse of THAT function. But still, because they are inverse function eln a= a and ln(ea)= a.

Well, to go even further, the only reason to call it a logarithm is because the integral behaves exactly like one, thus the properties of logarithms in general should have been studied before anything about Euler's number. :D
 

Similar threads

Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K