Question

Two circles are concentric if they have the same center.

On a coordinate plane, a circle has center (4, 6) and has a radius of 2 units.

Which equation represents a circle that is concentric with the circle shown but has a radius that is twice as large?

(x – 4)2 + (y – 6)2 = 4
(x – 4)2 + (y – 6)2 = 16
(x – 6)2 + (y – 4)2 = 16
(x – 6)2 + (y – 4)2 = 4

Answer 1

The radius doubles from 2 to 4, so r^2 = 16. The concentric circle is (x − 4)^2 + (y − 6)^2 = 16.