2x+y+3z=13 (1)
4x+2y+z=11 (2)
6x+y+4z=20 (3)
(1)×2-(2)
6z-z=26-11
5z=15
z=3
(3)-(1)
4x+z=7 (4)
x=(7-z)/4=1
y=13-2x-3z=2
所以x=1,y=2,z=3