|x|</ 3
x</ 3 sau x</ -3 => M={-3,-2,-1,0,1,2,3}
3</ x<6 => N={3,4,5}
MxN={(-3,3),(-3,4),(-3,5),(-2,3),(-2,4),(-2,5),(-1,3),(-1,4),(-1,5),(0,3),(0,4),(0,5),(1,3),(1,4),(1,5),(2,3),(2,4),(2,5),(3,3),(3,4),(3,5)}
NxM={(3,-3),(3,-2),(3,-1),(3,0),(3,1),(3,2),(3,3),(4,-3),(4,-2),(4,-1),(4,0),(4,1),(4,2),(4,3),(5,-3),(5,-2),(5,-1),(5,0),(5,1),(5,2),(5,3)}