x2+y2−x+2y−1=0x^{2}+y^{2}-x+2 y-1=0x2+y2−x+2y−1=0
x2+y2−3x+4y+1=0x^{2}+y^{2}-3 x+4 y+1=0x2+y2−3x+4y+1=0
x2+y2−2x+3y+k(x−y−1)=0x^{2}+y^{2}-2 x+3 y+k(x-y-1)=0x2+y2−2x+3y+k(x−y−1)=0
x2+y2−x+y−1=0x^{2}+y^{2}-x+y-1=0x2+y2−x+y−1=0