Question 757164
This equation has the standard form of a circle {{{(x-h)^2 + (y-k)^2 = r^2}}} where (h,k) is the center of the circle and r is the radius of the circle. 

Therefore for our above equation h = 2, k = 1, and r^2 = 9. Taking the positive squareroot of 9 we get that r = 3. {{{ sqrt(9) = 3 }}}

The center of the circle is at (2,1) and the radius of the circle is 3.