# Finding critical numbers

• Oct 14th 2012, 08:54 PM
neontiger94
Finding critical numbers
I am stuck on a question for my calc h.w

it reads to find the critical numbers of x^-2 ln x

When I took the derivative I got -2x^-3 lnx + x^-2 *1/x

I simplified and set it equal to zero. the critical numbers i got were 0 and e^1/2 however the question says I'm wrong
• Oct 14th 2012, 09:03 PM
MarkFL
Re: Finding critical numbers
What is the domain of the function?
• Oct 14th 2012, 09:58 PM
MaxJasper
Re: Finding critical numbers
Quote:

Originally Posted by neontiger94
it reads to find the critical numbers of x^-2 ln x
When I took the derivative I got -2x^-3 lnx + x^-2 *1/x
I simplified and set it equal to zero. the critical numbers i got were 0 and e^1/2 however the question says I'm wrong

This might apply:

http://mathhelpforum.com/attachment....1&d=1350280685
• Oct 14th 2012, 10:16 PM
neontiger94
Re: Finding critical numbers
sorry thats not correct it's x^-2 * lnx
• Oct 14th 2012, 10:19 PM
MarkFL
Re: Finding critical numbers
What is the domain of that function?
• Oct 14th 2012, 10:36 PM
MaxJasper
Re: Finding critical numbers
• Oct 15th 2012, 05:52 AM
alane1994
Re: Finding critical numbers
To find critical points, you find the derivative. Then you set the derivative equal to zero. You then solve for x. Those are then candidates for local maxima or minima.