# Exponential equation

• Apr 30th 2012, 05:28 PM
Bashyboy
Exponential equation
The problem is:

$e^{lnx} = 4$

Is there a way I can rewrite this to solve for x, or some rule that I am suppose to apply?
• Apr 30th 2012, 06:29 PM
skeeter
Re: Exponential equation
Quote:

Originally Posted by Bashyboy
The problem is:

$e^{lnx} = 4$

Is there a way I can rewrite this to solve for x, or some rule that I am suppose to apply?

note that $e^{\ln{x}} = x$
• Apr 30th 2012, 06:39 PM
Plato
Re: Exponential equation
Quote:

Originally Posted by Bashyboy
The problem is:
$e^{lnx} = 4$
Is there a way I can rewrite this to solve for x, or some rule that I am suppose to apply?

@Bashyboy,
Are you "jerking" our chain?
Are you playing us for 'fools'?
If you do not understand such a simple problem, why were you asked to solve it.
Personalty , I think you should be banded as a troll. You are wasting our time.
• May 1st 2012, 05:58 AM
Bashyboy
Re: Exponential equation
@Plato:
Well, clearly it is not a simple problem for me, especially seeing that I have not dealt with a problem like this for two semester. And if it is such a waste, why spend the time replying?

@Skeeter:
Now I believe I remember seeing something like this. And isn't true that the base e and the exponent go away because they are inverses? That's the part I have a little trouble wrapping my head around. That's the only explanation I have been given, and it just seem a good enough explanation for me.

What I started to do was: $ln(e)^{lnx} = ln(4)\rightarrow\ln(x)\times\ln(e) = ln(4)\rightarrow\ln(x) = ln(4)$, then finally $e^{ln(4)} = x$

which sort of brought me back to square one. I know I can just evaluate it in the calculator, but I don't know why the answer comes out the way it does.
• May 1st 2012, 09:15 AM
skeeter
Re: Exponential equation
$y = \ln{x}$

written as an equivalent exponential function ...

$x = e^y$

... but what is y in the first place?
• May 1st 2012, 11:37 AM
HallsofIvy
Re: Exponential equation
BashyBoy, I think that Plato was a bit annoyed that you would post a question like that, involving exponential and logarithms, without finding out, or reviewing, what exponentials and logarithms are. And the whole point of the problem is the definition of 'exponential' and 'logarithm'.