若x+y/x-y=6,把x,y的值都扩大二倍,则分式的值为 6 ；若xy/x-y=6 ,把x,y的值都扩大2倍,则分式的值为 12 .解题过程2x+2y/2x-2y=2（x+y）/2（x-y）=x+y/x-y=6xy/x-y=2x*2y/2x-2y=4xy/2（x-y）=2xy/x-y=12