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February 12th, 2016, 04:24 PM   #1
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Critical Value Help

Let f(x) = 8√x − 6x for x > 0. Find the open intervals on which f is increasing/(decreasing). Then determine the x-coordinates of all relative maxima/(minima).

Last edited by skipjack; February 13th, 2016 at 12:12 AM.
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February 12th, 2016, 05:00 PM   #2
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$f(x) = 8\sqrt{x} - 6x$

what did you get as the derivative?
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February 12th, 2016, 09:14 PM   #3
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I got f$\,'\!$(x) = 4x - 6 as the derivative.

Last edited by skipjack; February 13th, 2016 at 12:04 AM.
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February 12th, 2016, 09:23 PM   #4
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Not ${4 \over \sqrt x}-6$?
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February 13th, 2016, 05:11 AM   #5
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Quote:
Originally Posted by suhdude View Post
I got f$\,'\!$(x) = 4x - 6 as the derivative.
$f(x)=8x^{1/2}-6x$

try taking the derivative of the first term again using the power rule for derivatives ...

$y=kx^n$

$y'=knx^{\color{red}{n-1}}$
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