Question

the center of three congruent small circles are collinear, and their diameters form the diameter of the large circle, shown, whose area is 81 pi units. what is the circumference of one of the smaller circles? express your answer in simplest radical form.

Answer 1

let the radius of each of the smaller circles be r
so the radius of the larger circle is 3r
π(3r)^2 = 81π
9πr^2 = 81π
r^2 = 9
r=3

Circumf of smaller circle = 2πr = 6π