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Inverse of exponential function

by mark187
Tags: exponential, function, inverse
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mark187
#1
Sep17-11, 07:16 AM
P: 3
1. The problem statement, all variables and given/known data

Give the inverse of this function

N=f(L)=1816-8L

The answer has to be filled in in Maple

2. Relevant equations



3. The attempt at a solution

N=1816-8L

16-8L=ln(N)/ln(18)

-8L=(ln(N)/ln(18))-16

L=-ln(N)/(8*ln(18))+2

Is this correct?
When i fill this in in maple it's incorrect.
I've really no clue why it is wrong.
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ehild
#2
Sep17-11, 08:09 AM
HW Helper
Thanks
P: 10,668
L=-ln(N)/(8*ln(18))+2 is the same function as the original. Choose L the independent variable and N the dependent one. (Just exchange L and N).

ehild
Mentallic
#3
Sep17-11, 08:12 AM
HW Helper
P: 3,540
Yes it's correct. What are you typing into maple exactly? Your syntax is probably slightly off.

edit: Sorry I didn't notice that you forgot to swap your variables.

mark187
#4
Sep17-11, 09:13 AM
P: 3
Inverse of exponential function

thanks! It's also mentioned that it should be simplified as much as possible.

Does that mean that the 8*LN(18) could be simplified to 8*LN(2*9) and more?
Mentallic
#5
Sep17-11, 10:08 AM
HW Helper
P: 3,540
It's as simple as it can get, unless you believe [itex]\ln{\frac{1}{x}}[/itex] is more simple than [itex]-\ln{x}[/itex] you shouldn't be changing anything.

[itex]\ln{18}[/itex] is definitely more desirable than [itex]\ln{9\cdot2}[/itex]
Ray Vickson
#6
Sep17-11, 12:06 PM
Sci Advisor
HW Helper
Thanks
P: 5,086
Quote Quote by mark187 View Post
1. The problem statement, all variables and given/known data

Give the inverse of this function

N=f(L)=1816-8L

The answer has to be filled in in Maple

2. Relevant equations



3. The attempt at a solution

N=1816-8L

16-8L=ln(N)/ln(18)

-8L=(ln(N)/ln(18))-16

L=-ln(N)/(8*ln(18))+2

Is this correct?
When i fill this in in maple it's incorrect.
I've really no clue why it is wrong.
When I let Maple solve the equation for L it gives me exactly what you wrote. Why do you think Maple thinks it is incorrect… What type of error message are you receiving…

That annoying … is actually a question mark, but when I type it in it gives me that accented E; that only seems to happen when I access this website through Google Chrome!

RGV
mark187
#7
Sep17-11, 05:27 PM
P: 3
Quote Quote by Ray Vickson View Post
When I let Maple solve the equation for L it gives me exactly what you wrote. Why do you think Maple thinks it is incorrect… What type of error message are you receiving…

That annoying … is actually a question mark, but when I type it in it gives me that accented E; that only seems to happen when I access this website through Google Chrome!

RGV
Well, this assignment was given in a little online test.
The point is, that i can't see why the answer was wrong.
I have 2 chances, so for the second change i will try to swap the variables.


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