Question 644233
{{{(1/x - 1/y)/(1/x + 1/y)}}}  


{{{((1*y - 1*x)/xy)/((1*y + 1*x)/xy)}}} 


{{{((y - x)/cross(xy))/((y + x)/cross(xy))}}} 


{{{(y - x)/(y + x)}}} .....that is different than your result {{{(x-y)/(x+y)}}} 


all you can do now is to rearrange terms


{{{(-x+y)/(x + y)}}} 


{{{-(x-y)/(x + y)}}}