7x=y8 ⇒x = 8, y = 7
xx=y2 ⇒x=2, y=2; x=4, y =8;
5y7< 50x ⇒y=0 si x=8 si 9
2xy> 289 ⇒x=9 si y =0,1, 2,3,4,5,6,7,8,9
72x398 < 724y28 ⇒x= 4, si y= 4, 5, 6,7, 8, 9
x= 3 si y = 0,1,2,3,4,5,6,7,8,9
x= 2 si y = 0,1,2,3,4,5,6,7,8,9
x= 1 si y = 0,1,2,3,4,5,6,7,8,9
x= 0 si y = 0,1,2,3,4,5,6,7,8,9