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

[scrum]

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.

 

[galactus]

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

 

[scrum]

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.