1.
z=3y/2
把:z=3y/2代入x+y+z=3y
得:x+y+3y/2=3y
整理后得:x=y/2
所以:x/(x+y+z)=(y/2)/(y/2+y+3y/2)=1/6
2.
因为1/x-1/y=3,则1/y-1/x=-3
(2x+3xy-2y)/(x-2xy-y) (分子分母同时除以xy)
=(2/y+3-2/x)/(1/y-2-1/x)
=(2/y-2/x+3)/(1/y-1/x-2)
=(-2*3+3)/(-3-2)
=-3/-5
=3/5