X二次方+2X+Y二次方-6y+10=0 x^2+2x+1+y^2-6y+9=0 (x+1)^2+(y-3)^2=0 (x+1)^2=0 (y-3)=0 x+1=0 y=3 x=-1所以2x-y=2*(-1)-3 =-2-3 =-5