x(y+1)-y-1=5-1
(x-1)(y+1)=4
x>0,x-1>-1
y>0,y+1>1
即x-1非负
所以4=1*4=2*2
则x-1=1,y+1=4或x-1=y+1=2
所以x=2,y=3
x=3,y=1