若1/x-1/y=1,求3y-xy-3x/x-xy-y的值.若x/2=y/3=z/4不等于0,求x-y-z/3x+2y-

(3y-xy-3x)/(x-xy-y)
分子 分母同除xy
=(3y/xy-xy/xy-3x/xy)/(x/xy-xy/xy-y/xy)
=(3/x-1-3/y)/(1/y-1-1/x)
=(3-1)/(-1-1)
=-2
(x-y-z)/(3x+2y-z)
分子 分母同除6
=(x/6-y/6-z/6)/(3x/6+2y/6-z/6)
=((1/3)(x/2)-(1/2)(y/3)-z/6)/(x/2+y/3-z/6)
=((1/3)(z/4)-(1/2)(z/4)-z/6)/(z/4+z/4-z/6)
=((1/3)(1/4)-(1/2)(1/4)-1/6)/(1/4+1/4-1/6)
=(1/12-1/8-1/6)/(1/2-1/6)
=((2-3-4)/24))/((3-1)/6)
=(-5/24)/(1/3)
=-5/8