1.3x/(x-3)²-x/3-x =3x/(x-3)²+x/(x-3)=3x/(x-3)²+(x²-3x)/(x-3)²=x²/(x-3)².2.x²+xy/x-y÷xy/x-y =x（x+y)/x-y×（x-y)/xy=(x+y)/y.3.(a/a-1-2/a-1)÷(1-1/a+1) =(a-2/a-1...