问题补充：
约分2X^2Y(X-Y)/12XY^2(Y-X) 通分1/a^2-3a与1/a^2-9 通分1/2x-2与1/(x-1)^2约分2X^2Y(X-Y)/12XY^2(Y-X)通分1/a^2-3a与1/a^2-9通分1/2x-2与1/(x-1)^2通分1/（x+1）^2与2/x^2-1与3/(x-1)(x-2)
答案：
2X^2Y(X-Y)/12XY^2(Y-X)
=－X/(6Y）
1/(a^2-3a)=1/[a(a-3)]=(a+3)/[a(a-3)(a+3)]
1/a^2-9=a/[a(a-3)(a+3)]
1/(2x-2)=(x-1)/[2(x-1)^2]
1/(x-1)^2=2/[2(x-1)^2]
1/(x+1)^2=(x-1)(x-2)/[(x+1)^2(x-1)(x-2)]
2/(x^2-1)=2(x+1)(x-2)/[(x+1)^2(x-1)(x-2)]
3/(x-1)(x-2)=3(x+1)^2/[(x+1)^2(x-1)(x-2)]
