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Annulus

An annulus is the region between two concentric circles, an inner and an outer circle, both having the same center point but with different radiuses.
Drawing of an annulus

Area of an annulus

The area of an annulus can be calculated with the formula:

A=pi*(R^2-r^2)

Where R is the radius of the outer circle and r is the radius of the inner circle.

Calculate the area of an annulus

Inner circle's radius (r): 
Outer circle's radius (R): 
Pi: