x + y - 2z = 0

Z_5

0 * 2 = 0  0 / 2 = 0
1 * 2 = 2  2 / 2 = 1
2 * 2 = 4  4 / 2 = 2
3 * 2 = 1  1 / 2 = 3
4 * 2 = 3  3 / 2 = 4

xy x+y z
--------
14  0  0
23  0  0
32  0  0
41  0  0
01  1  3
10  1  3
24  1  3
42  1  3
02  2  1
20  2  1
34  2  1
43  2  1
03  3  4
12  3  4
21  3  4
30  3  4
04  4  2
13  4  2
31  4  2
40  4  2