October 21st, 2012, 06:49 PM  #1 
Newbie Joined: Oct 2012 Posts: 11 Thanks: 0  Change of rate
I tried the dy/dt formula and steps, but I can't seem to get any of the answer choices. Question: a point's moving on a graph of 4x^(3)+6x^(3)=xy. When at Point ((1/10),(1/10)), the x coord is decreasing by 4 u/s... what's the speed of Y coordinate? Choices: 2,1,2,1 or 0 units/sec If you know a similar prob or anything, that would be great for help. 
October 21st, 2012, 07:20 PM  #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  Re: Change of rate
I suspect you have mistyped the given curve. You want to differentiate with respect to time t, then solve for and plug in the given values for . If you can correct the equation of the curve, I will be glad to help. 
October 22nd, 2012, 01:55 PM  #3  
Math Team Joined: Sep 2007 Posts: 2,409 Thanks: 6  Re: Change of rate Quote:
However, if x= 1/10, then you would, in fact, have 10(1/1000)= 1/100= (1/100)(1/100) so that may well be what is intended. Quote:
 
March 8th, 2013, 06:35 AM  #4 
Global Moderator Joined: Dec 2006 Posts: 20,969 Thanks: 2219 
If the intended equation is 4x³ + 6y³ = xy, one gets 1 units/sec as the answer.


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