# Determining absolute extreme of function

• Nov 7th 2012, 07:50 PM
Chaim
Determining absolute extreme of function
f(x)=x2+2x-4 Interval is [-1, 1]
What I did:
f'(x)=2x+2
x=-1
Plugged in:
One of my minimums is (-1, 0)

I'm confused on how to get the maximum now.
I did 0=x2+2x-4
4=x(x+2)
4/(x+2)=x
But I don't think this is correct.

Thanks!
• Nov 7th 2012, 08:28 PM
Prove It
Re: Determining absolute extreme of function
Global maxima and minima can occur either at stationary points or at endpoints of the function. You have found the stationary point. Now evaluate each of the endpoints and see which of the three values is the largest and which is the smallest.
• Nov 11th 2012, 09:47 PM
Chaim
Re: Determining absolute extreme of function
Quote:

Originally Posted by Prove It
Global maxima and minima can occur either at stationary points or at endpoints of the function. You have found the stationary point. Now evaluate each of the endpoints and see which of the three values is the largest and which is the smallest.

Ok still kind of confused, like for example, if I had -x^2 + 3x and the Intervals are [0,3]
What I did was find the derivative which is -2x + 3, and so x=3/2
I plugged that back into the original equation, so the maximum is ((3/2),(9/4))

The minimums are (0,0) and (3,0), but I'm a bit confused how they got to the minimum
Just like with this problem as well.
I kind of need help, so a little more advice would be nice :)
Thanks!
• Nov 12th 2012, 09:44 PM
hollywood
Re: Determining absolute extreme of function
Like ProveIt said, you need to look at the points where the derivative is zero and ALSO the endpoints. You got a maximum where the derivative is zero, and the minima come from the endpoints.

- Hollywood