Related Rates: Find dA/dt in terms of dr/dt for circle

scrum

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Oct 11, 2007
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This is a related rate problem I have.

I don't really understand what is going on. I looked at the examples in the book but I don't really see how they relate to the problem I am doing.

the answers I get for part one are 2pi(s) which is the derivative of the area of a circle, but that is returned as wrong.

Just looking for prod in right direction.
 
Another over used related rates problem. But easy, by comparison.


How are you getting 2Pi?.

We want dA/dt when r=22 and dr/dt=1.

\(\displaystyle \L\\A={\pi}r^{2}\)

\(\displaystyle \L\\\frac{dA}{dt}=2{\pi}r\frac{dr}{dt}\)

Now, fill in your knowns and solve for dA/dt
 
I see what you did there.

I was messing up with the fact that it was implicit differentiation so I was trying
2pi(r) and 2(pi)(dr/dt) but not 2pi (r)(dy/dt)

so i fixed it and then did 44pi for part two and got them correct.

I hate these word problems they are all different and I don't know how to set up equations.
 
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