HELP! C3 Connected Rates Of Change Question Watch

bananas1234
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Report Thread starter 13 years ago
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I am stuck on a question about connected rates of change for C3. The question is as follows:

The radius of a circle is increasing at a constant rate of 0.2 cm s-1

a) Show that the perimeter of the circle is increasing at the rate of 0.4π cm s-1.

b) Find the rate at which the area of the circle is increasing when the radius is 10cm.

c) Find the radius of the circle when its area is increasing at the rate of 20 cm2 s-1.

I have managed to answer a) and b) I just do not have a clue about c) SOMEONE PLEASE HELP ME!!! :confused: (π=Pi≈3.14)
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unknown1557
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Area increasing rate= 20

so dA/dt=20

dA/dt=dA/dr *dr/dt

dA/dr=2πr

dr/dt=0.2

20=2πr * 0.2

r=100/2π

i think thats it
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bananas1234
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Report Thread starter 13 years ago
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(Original post by unknown1557)
Area increasing rate= 20

so dA/dt=20

dA/dt=dA/dr *dr/dt

dA/dr=2πr

dr/dt=0.2

20=2πr * 0.2

r=100/2π

i think thats it
Thank you very much sir...much appreciated
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