My Math Forum finding dy/dt

 Calculus Calculus Math Forum

 March 8th, 2017, 10:26 AM #1 Newbie   Joined: Mar 2017 From: Yes Posts: 2 Thanks: 0 finding dy/dt dy/dt = x^2 + xy -y^2 and dx/dt = 8 when x = 6 Whenever I seem to try to do this problem, I can't get the y at the end to cancel and if I do it never is the correct answer. Last edited by skipjack; March 8th, 2017 at 11:34 AM.
 March 8th, 2017, 11:06 AM #2 Senior Member     Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs Is that the entirety of the information you were given?
 March 8th, 2017, 11:34 AM #3 Newbie   Joined: Mar 2017 From: Yes Posts: 2 Thanks: 0 yes
 March 8th, 2017, 11:53 AM #4 Global Moderator   Joined: Dec 2006 Posts: 20,747 Thanks: 2133 You are told (but omitted to tell us) that y > 0, so when x = 6, y must equal 9. Substituting y = 9 in your answer gives dy/dt = (-96 - 72)/(6 - 18) = 14. The above assumes the intended question is "Find dy/dt where x² + xy - y² = 9 and dx/dt = 8 when x = 6". Last edited by skipjack; March 12th, 2017 at 06:17 AM.
March 12th, 2017, 04:42 AM   #5
Math Team

Joined: Jan 2015
From: Alabama

Posts: 3,264
Thanks: 902

Quote:
 Originally Posted by wilkin823 dy/dt = x^2 + xy -y^2

Is this really "dy/dt" or is it the original function, y, for which you want to find the derivative?
Quote:
 and dx/dt = 8 when x = 6
Quote:
 Whenever I seem to try to do this problem, I can't get the y at the end to cancel and if I do it never is the correct answer.

 Tags dy or dt, finding

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post selkat01 Calculus 2 September 3rd, 2014 01:29 AM mathkid Calculus 3 October 30th, 2012 09:00 AM chocolate Algebra 4 July 2nd, 2012 12:51 PM ilovetheflowguy Algebra 3 November 14th, 2011 12:17 PM im_with_stupid Algebra 6 January 26th, 2011 01:01 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top