已知x平方+y平方－4x+6y+13=0,求xy的值. (x^2-4x+4)+(y^2+6y+9)=0 (x-2)^2+(y+3)^2=0 x-2=0 y+3=0 x=2 y=-3 xy=-6,7,x^2+y^2-4x+6y+13=0 (x^2-4x+4)+(y^2+6y+9)=0 (x-2)^2+(y+3)^2=0 x=2 y=-3,0,
