# Solving inverse function

• Sep 19th 2010, 04:36 PM
iamanoobatmath
Solving inverse function
Hello I am having difficulty solving this question. Any help would be greatly appreciated.
$g(x)=3+x+e^x$
The e is the mathematical constant not a variable

find $g^{-1}(4)$

So I must find a value of x where g(x)=4

this is my attempt:
$4=3+x+e^x$
$1=x+e^x$
$1-x=e^x$
I know that ln(e^x)=x so I thought of doing that
ln(1-x)=x
But I don't know what to do after that. Thanks for the assistance.
• Sep 19th 2010, 04:41 PM
Chris L T521
Quote:

Originally Posted by iamanoobatmath
Hello I am having difficulty solving this question. Any help would be greatly appreciated.
$g(x)=3+x+e^x$
The e is the mathematical constant not a variable

find $g^{-1}(4)$

So I must find a value of x where g(x)=4

this is my attempt:
$4=3+x+e^x$
$1=x+e^x$
$1-x=e^x$
I know that ln(e^x)=x so I thought of doing that
ln(1-x)=x
But I don't know what to do after that. Thanks for the assistance.

At this stage, I can only complete it by observation:

If $x=0$, then $1-0=e^0\implies 1=1$

So $g^{-1}(4)=0$
• Sep 19th 2010, 11:27 PM
mr fantastic
Quote:

Originally Posted by Chris L T521
At this stage, I can only complete it by observation:

If $x=0$, then $1-0=e^0\implies 1=1$

So $g^{-1}(4)=0$

Undoubtedly a solution by inspection was intended.