Center (0,4) passes through the point (1,4) (1) (h,k) = (0,4) so plug those in: (2) Now all we need is r2 So we plug in (x,y) = (1,4) in (2) So plug in 1 for r2 in (2) and you have the answer: or you can just write x2 instead of (x-0)2 Edwin