[(xy+2)(xy-4)-(2xy)²+8]÷xy=[(xy)^2-2xy-8-(2xy)²+8]÷xy=[-(xy)^2-2xy]÷xy=-xy-2其中x=1/8 y=-3所以:[(xy+2)(xy-4)-(2xy)²+8]÷xy=3/8-2=-13/8
把(xy+2)(xy-4)乘开