x的2次方+y的2次方-4x+6y+13=0(x^2-4x+4)+(y^2+6y+9)=0(x-2)^2+(y+3)^2=0因为(x-2)^2>=0 (y+3)^2>=0所以(x-2)^2=0 (y+3)^2=0 x-2=0 y+3=0 x=2 y=-3 所以xy=2*(-3)...
