Why is the derivative of a circle's area its perimeter?

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Homework Statement



Explain why the relationship of the derivative of a Circle's area is its perimeter makes sense.

Homework Equations



Area of a Cirle=pi*r^2

The Attempt at a Solution


da/dr=2pi*r
2r=diameter and the circumfrece=pi*D so da/dr=Circumfrence
How do i explain why this works?
 
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No idea? Draw a circle of radius r and a circle of radius r+dr. Can't you see a geometric way to approximate the difference in the areas?
 

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