Math

I have a practice question that I am stuck on and need help.

A certain insect pest has infested a cornfield. The pests are spreading through the field in a circular pattern at the rate of 3m/day. When the radius of the infested area is 70m. How fast is the area of the infested region increasing at that moment?



The answer is 420(pi)m^2 /day

I know it has to do with derivatives and rates of change, but I'm having trouble finding the connection for this one.

area-PI r^2
d area/dtime= 2PI r dr/dt

plug the numbers, and solve.

is that area - pir^2?

as in negative?

we use the ^ to say exponent.

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asked by Dave

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