x^2+y^2-2x+y+k=0
x^2-2x+1-1+y^2+y+1/4-1/4+k=0
(x-1)^2+(y+1/2)^2-5/4+k=0
(x-1)^2+(y-1/2)^2=5/4-k
5/4-k>0
k