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October 21st, 2012, 06:49 PM   #1
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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.
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October 21st, 2012, 07:20 PM   #2
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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.
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October 22nd, 2012, 01:55 PM   #3
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Re: Change of rate

Quote:
Originally Posted by allylee
I tried the dy/dt formula and steps, but I can't seem to get any of the answer choices

Question:a points moving on a graph of 4x^(3)+6x^(3)=xy.
MarkFL suspects you have copied this incorrectly because it would be more simply written 10x^3= xy.
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:
When at Point ((1/10),(1/10)), the x coord is decreasing by 4 u/s...whats 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
For any y as a function of x, by the chain rule, . So, whatever your formula is, differentiate with respect to x to find dy/dx.
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March 8th, 2013, 06:35 AM   #4
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If the intended equation is 4x + 6y = xy, one gets -1 units/sec as the answer.
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