May 8th, 2009, 05:39 PM  #1 
Member Joined: May 2009 Posts: 58 Thanks: 0  Definite Integrals, extrema
Find and classify the relative maxima and minima of f(x), if f(x) = integral from 0 to x of {(t^24)dt} /{1+(cost)^2} I got x=2 and x=2 for f'(x)=0, but, I don't know how to calculate the relative maxima and minima. Please help me. Thank you 
May 9th, 2009, 09:07 AM  #2 
Senior Member Joined: Dec 2008 Posts: 251 Thanks: 0  Re: Definite Integrals, extrema
Here, we may use the fact that (As you move to the right, the rate of change of the area under a curve is equal to the height of the function.) Your solutions are correct. To prove that they are relative maxima and minima, we can use the Second Derivative Test: 
May 10th, 2009, 04:53 AM  #3 
Member Joined: May 2009 Posts: 58 Thanks: 0  Re: Definite Integrals, extrema
Thanks for your help. But, how can I calculate f(2)? is x=2 also a solution since the domain of f(x) is x>=0 ?

May 10th, 2009, 05:23 AM  #4 
Senior Member Joined: Dec 2008 Posts: 251 Thanks: 0  Re: Definite Integrals, extrema
If the domain is, as you say, , then is the only local extremum. However, since is squared and added to in the denominator, is defined everywhere. I just put the integral into the Wolfram Online Integrator and it gave an answer that was not expressed in terms of elementary functions. If the problem only asks to classify the extrema, then I don't think you have to worry about the values of the extrema at those points. 

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