The radius of a circular oil slick on the surface of a pond is increasing at the rate of 10 meters/min. At what rate is the circle's area changing when the radius of the oil slick is 20 m. ?
"10\\ m\/min=0.167\\ m\/s"
"\\Delta A=A_0-A=\\pi R_0^2-\\pi(R_0+0.167\\cdot1)^2=3.14\\cdot20^2-3.14\\cdot(20+0.167\\cdot1)^2="
"=21\\ (m^2\/s)". Answer
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