Concentric Circles

The circles in the figure are concentric. The chord is tangent to the inner circle and has length 12. What is the area of the non-shaded region?
Source: NCTM Mathematics Teacher, November 2006

area of large circle =\pi r^2
area of inner circle =\pi x^2
area of non-shaded region=area of large circle – area of inner circle
=\pi r^2-\pi x^2
=\pi 36

Answer: 36\pi

About mvtrinh

Retired high school math teacher.
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