# Absolute Extrema

• April 16th 2010, 09:33 AM
cokeclassic
Absolute Extrema
I have a question regarding Absolute Extrema.

f(x) = 7xlnx

Find the absolute extrema. For the answer, my professor got 1/e. I do not understand the last step of this. He had lnx = -1 and then he turned it into
e^lnx = e^-1, which followed x = e^-1. Is there any link with x and e ^lnx I am missing?

Thanks
• April 16th 2010, 09:41 AM
AllanCuz
Quote:

Originally Posted by cokeclassic
I have a question regarding Absolute Extrema.

f(x) = 7xlnx

Find the absolute extrema. For the answer, my professor got 1/e. I do not understand the last step of this. He had lnx = -1 and then he turned it into
e^lnx = e^-1, which followed x = e^-1. Is there any link with x and e ^lnx I am missing?

Thanks

$e^{ln[f(x,y)]} = f(x,y)$

by rule of logs. The base of ln is e so when we raise the base to ln, we simply get the above.