## Elementary Geometry for College Students (6th Edition)

$A_{ring} = \pi BC^2$
We call r the radius of the smaller circle. The radius of the larger circle is: $R = \sqrt{BC^2 + r^2}$ Thus, the area of the ring is: $A = \pi (R^2 - r^2) \\ A = \pi (BC^2 + r^2 - r^2) = \pi BC^2$