⑴原式=Y/(14X-Y)
⑵原式=1/(a-b)
⑶原式=(X+Y)/2
⑷4 a^3(X-Y)/9.要过程！分子与分母分别分解因式，然后约分。⑴原式=3XY/［3X(14-Y)］=Y/(14-Y)⑵原式=(a-b)/[(a+b)(a-b)]=1/(a+b)⑶原式=(X+Y)^2/［2(X+Y)］=(X+Y)/2⑷原式=12a^3(X-Y)^2/27(X-Y)=4a^3(X-Y)/9.