|x-y+1|-2|y-x-3|+|y-x|+5
=|x-y+1|-2|x-y+3|+|x-y|+5
若x-y>0
则x-y+1>0
x-y+3>0
|x-y+1|-2|y-x-3|+|y-x|+5
=x-y+1-2x+2y-6+x-y+5
=0
若-10
|x-y+1|-2|y-x-3|+|y-x|+5
=x-y+1-2x+2y-6+y-x+5
=-2x+2y
若-3