x+y+z=2 (1)
x-2y+z=-1 (2)
x+2y+3z=-1 (3)
(1)-(2)
3y=3
y=1
(3)-(1)
y-2z=-3
z=(y+3)/2=2
x=2-y-z=-1
所以x=-1,y=1,z=2