过N(1,2)的切线方程为x+2y+x+1-3(y+2)+5=0,即2x-y=0.设圆方程为
x^2+y^2+2x-6y+5+a(2x-y)=0,点M(3,-1)代入,得a=-27/7.
得所求圆方程x^2+y^2+2x-6y+5-27/7 (2x-y)=0
过N(1,2)的切线方程为x+2y+x+1-3(y+2)+5=0,即2x-y=0.设圆方程为
x^2+y^2+2x-6y+5+a(2x-y)=0,点M(3,-1)代入,得a=-27/7.
得所求圆方程x^2+y^2+2x-6y+5-27/7 (2x-y)=0