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GeomBench
Outer circle's area minus the inner circle's area.
An annulus is the region between two concentric circles — just take the big circle's area and subtract the small one's: A = π(R² − r²).
Washers, pipes viewed end-on, running tracks, and CD/DVD discs are all annuli — this same subtraction trick works for any of them.
Ring area
122.522
What you entered
Outer circle area
π × 8²= 201.0619Inner circle area
π × 5²= 78.5398Ring area = outer − inner
201.0619 − 78.5398= 122.5221Result
Ring area: 122.522
A ring with outer radius 8 and inner radius 5 has an area of 122.522 — the outer circle's area minus the inner circle's area.