x(y+1)+(y+1)-1=6
(x+1)(y+1)=7
<=>x+1=7va y+1=1
hoacx+1=-7va Y+1=-1
hoacx+1=1va y+1=7
hoacx+1=-1va y+1=-7
Kho..................wa.....................troi.....................thi......................lanh.................ret.......................ai........................tich..........................ung.....................ho........................minh.....................cho....................do....................lanh