当1+X与1+Y互为倒数,且XY≠0,则1/X-1/Y=?
1/X-1/Y=(X+Y)/XY 先乘以XY在除以XY
(1+X)(1+Y)=1解得
1+X+Y+XY=1则x+y=xy
所以1/x-1/y=(xy)/(xy)=1