1道数学题 答对有加分 要详细的过程！！！

1/x-1/y=3

5x+xy-5y/x-xy-y
分子分母同除以xy
=(5/y+1-5/x)/(1/y-1-1/x)
=[-5(1/x-1/y)+1]/[-(1/x-1/y)-1]
=(-5*3+1)/(-3-1)
=7/2

x-xy-y连在一起吗？？

解:因为1/x-1/y=3 所以y-x/xy=3 所以设x-y=-3k 则xy=k
那么5x+xy-5y/x-xy-y
=5x-5y+xy/x-y-xy
=-3k*5+k/-3k-k
=-14k/-4k
=7/2