矩阵方法：
1 1 1 36
12 8 5 201
1 1 1 36
0 - 4 - 7 - 231
1 1 1 36
0 4 7 231
==>
x + y + z = 36
4y + 7z = 231
令x = 3n
z = 36 - y - 3n
4y + 7(36 - y - 3n) = 231
- 3y + 252 - 21n = 231
3y = 21 - 21n
y = 7 - 7n
z = 36 - (7 - 7n) - 3n
= 4n + 29
所以方程的解为：
x = 3n,y = 7 - 7n,z = 4n + 29,n∈Z有没有正整数解？x = 3n，y = 7 - 7n，z = 4n + 29没有正整数解若x>0,则n>0但若y>0,则n<0所以没有正整数解