Annulus
An annulus is a flat shape like a ring. Its edges are two circles that have the same center. |
The face of a metal washer is an annulus
Something shaped like an annulus is said to be annular.
Saturn has annular rings:
Area
Because it is a circle with a circular hole, you can calculate the area by subtracting the area of the "hole" from the big circle's area:
Area = πR2 − πr2
= π( R2 − r2 )
= π( R2 − r2 )
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