1、3x/（x-3）²+x/x-3=[3x+x(x-3)]/(x-3)²=(3x+x²-3x)/(x-3)²=x²/(x-3)²2、（1+1/x-2）÷x²-1/2x-4=[(x-1)/(x-2)]×[2(x-2)/(x+1)(x-1)]=2/(x+1)3、若1/x-1/y=2,求3x-2xy-3y/x-2...