x^2+y^2-2x+4y+5=0(x^2-2x+1)+(y^2-4y+4)=0(x-1)^2+(y-2)^2=0因为(x-1)^2>=0 ,(y-2)^2>=0所以(x-1)^2=0 ,(y-2)^2=0x=1 y=2所以y(x^2-x)+x^2*(5-y)-9=2*(1-1)+1*(5-2)-9=0+3-9=-6