原式=(xy*xy-4-4xy*xy+4)/(xy)=-3xy
[(xy+2)(xy-2)-2(x^2)(y^2)+4]/冲渗xy=[(x^2)(y^2)-4-2(x^2)(y^2)+4]/xy=-(x^2)(y^2)/散念脊高庆xy=-xy
=(x^2y^2-4-2x^2y^2+4)/(xy)=(-x^2y^2)/(xy)=-xy