Question

已知x分之一减y分之一等于2,求2x-xy-2y分之x+4xy-y的的值 尽量不要用符号

Answer 1

1/x-1/y=2 => (y-x)/xy=2, => y-x=2xy => x-y=-2xy
(2x-xy-2y)/(x+4xy-y)
={2(x-y)-xy}/{(x-y)+4xy}
=(-4xy-xy)/(-2xy+4xy)
=-5xy/2xy
=-5/2