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December 3rd, 2008, 06:23 AM   #1
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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!!!
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December 3rd, 2008, 07:30 AM   #2
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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].
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December 3rd, 2008, 01:16 PM   #3
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Re: multiple choice related rate problem please help

oh whoops thanks for catching that
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