xy+x+y = 3
<=> (xy+x)+(y+1) = 4
<=> (y+1).(x+1) = 4
Tương tự : (y+1).(z+1) = 9 ; (z+1).(x+1) = 16
=> 4.9.16 = [(x+1).(y+1).(z+1)]^2
<=> [(x+1).(y+1).(z+1)]^2 = 576
<=> (x+1).(y+1).(z+1) = -24 hoặc (x+1).(y+1).(z+1) = 24
<=> x+1 = -8/3 ; y+1 = -3/2 ; z+1 = -6 hoặc x+1 = 8/3 ; y+1 = 3/2 ; z+1 = 6
<=> x=-11/3 ; y=-5/2 ; z=-7 hoặc x=5/3 ; y=1/2 ; z=5
<=> x+y+z = -79/6 hoặc x+y+z = 43/6
Vậy ................
P/S : Tham khảo nha