The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry. 
Home Analytic Geometry Circle and Ellipse Annulus (Circle Ring)  
Search the VIAS Library  Index  
Annulus (Circle Ring)An annulus is the region between two concentric circles. The area of the annulus formed by two circles of radii r_{i} and r_{o} is given by The mean radius rm is defined by the following equation: It can be shown that the area of the annulus is equal to the area of the circle whose diameter is tangent to the inner circle (point C) and whose radius is the line segment between point C and the intersection of the tangent and the outer circle (points A and B).


Home Analytic Geometry Circle and Ellipse Annulus (Circle Ring) 