# 1. b) Find the rate of change of the area of a circle with respect to its radius r when  r = 4 cm

Area of the circle (A) =
Rate of change of the area of a circle with respect to its radius r =  =  =
So, when r = 4, Rate of change of the area of a circle =   =
Hence, Rate of change of the area of a circle with respect to its radius r when r = 4 is

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