a + b + c =12 2a - b + 2c =12 3a + 2b - c =8

jawab

a + b + c = 12
2a - b + 2c = 12 |(+)
3a + 3c = 24
a + c = 8 (pers 1)

a + b + c= 12 } kali 2
3a + 2b - c = 8

2a+ 2b + 2c = 24
3a + 2b - c = 8  |(+)
5a + c = 32   (pers.2)

a + c = 8
5a + c = 32 | (-)
-4a = - 24
a = 6

c = 8-a = 8-6
c = 2

a + b + c = 12
6 + b + 2 = 12
8 + b = 12
b= 4
(a,b,c)= (6, 4,2 )

Jadi, himpunan penyelesaiannya = {2,4,6}