# Derivative of the Area of a Circle

by husky88
Tags: circle, derivative
 P: 79 1. The problem statement, all variables and given/known data Show that the rate of change of the area of a circle with respect to its radius is the same as the circumference of the circle. Can you suggest why? 2. Relevant equations A = $$\pi$$r$$^{2}$$ = f(r) L = 2$$\pi$$r = g(r) 3. The attempt at a solution I have showed that the derivative of f(r) is equal to g(r). But I have no idea why the area and the circumference of the circle are related in such a way. Any suggestions greatly appreciated. Thank you.
 P: 52 Start by thinking about what any derivative of a function is describing in general, and then how it applies here specifically.
 P: 79 The derivative describes the slope of a tangent to the circle which is perpendicular to the radius... but I don't seem to go anywhere from here... hmmm

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