Calculus Calculus Math Forum

 February 12th, 2016, 04:24 PM #1 Newbie   Joined: Feb 2016 From: Oregon Posts: 19 Thanks: 0 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. February 12th, 2016, 05:00 PM #2 Math Team   Joined: Jul 2011 From: Texas Posts: 3,101 Thanks: 1677 $f(x) = 8\sqrt{x} - 6x$ what did you get as the derivative? February 12th, 2016, 09:14 PM #3 Newbie   Joined: Feb 2016 From: Oregon Posts: 19 Thanks: 0 I got f$\,'\!$(x) = 4x - 6 as the derivative. Last edited by skipjack; February 13th, 2016 at 12:04 AM. February 12th, 2016, 09:23 PM #4 Math Team   Joined: Dec 2013 From: Colombia Posts: 7,700 Thanks: 2682 Math Focus: Mainly analysis and algebra Not ${4 \over \sqrt x}-6$? February 13th, 2016, 05:11 AM   #5
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Quote:
 Originally Posted by suhdude 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 ...

$y=kx^n$

$y'=knx^{\color{red}{n-1}}$ Tags critical, critical value Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post mathe Calculus 2 November 11th, 2015 01:32 PM mathbalarka Calculus 4 December 29th, 2012 05:40 AM mathkid Calculus 1 November 11th, 2012 07:34 PM Calc12 Calculus 9 December 14th, 2010 09:18 PM symmetry Advanced Statistics 0 May 2nd, 2007 04:13 PM

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