Problem: The area of the ring between two concentric circles is 1221​π square inches. The length of a chord of the larger circle tangent to the smaller circle, in inches, is:
Answer Choices:
A. 2​5​
B. 5
C. 52​
D. 10
E. 102​
Solution:
Let R be the larger radius, let r be the smaller radius, and let L (inches) be the length of the chord. Then R2−r2=(2L​)2. Since πR2−πr2=225π​,R2−r2=225​.