[(xy+2)(xy+2)-2(xy+1)+2]÷(xy)=[(xy+2)(xy+2)-2xy-2+2]÷(xy)=[(xy+2)(xy+2)-2xy]÷(xy)=[(xy)^2+4xy+4-2xy]÷(xy)=[(xy)^2+2xy+4]÷(xy)根据题意可知,x,y均不为0所以,上式=xy+2+4/xy因为xy=-0.4,带入得原式=-8.4...xy+2 2怎么来的[(xy)^2+2xy+4]÷(xy)=xy+2+4/xy