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December 3rd, 2008, 06:23 AM  #1 
Newbie Joined: Nov 2008 Posts: 12 Thanks: 0  multiple choice related rate problem please help
A point moves on the curve 3x^2  8y^2 = 16 so that its y coordinate increases at the constant rate of 14 meters per second. At what rate is the x coordinate changing when x = 4 meters? Assume y > 0. [A] 7 m/s [B] 21/8 m/s [C] 56/3 m/s [D] 7/2 * sqrt (2) m/s I've tried implicit on the problem as it is which is 6x(dx/dt) + 16y(dy/dt) = 0... I plugged x = 4 into the original equation to find out that y = 2... then I plugged in all the information and solved for (dx/dt), but i ended up with 472 m/s please help!!! 
December 3rd, 2008, 07:30 AM  #2 
Senior Member Joined: Jul 2008 Posts: 895 Thanks: 0  Re: multiple choice related rate problem please help
Well, I'd try 6x(dx/dt) [color=#FF0000][/color] 16y(dy/dt) = 0 if the original is correct. Otherwise you are on the right track, and the answer should be part [C]. 
December 3rd, 2008, 01:16 PM  #3 
Newbie Joined: Nov 2008 Posts: 12 Thanks: 0  Re: multiple choice related rate problem please help
oh whoops thanks for catching that


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