x+y+z=26 (1)
x-y=1 (2)
2x-y+z=18(3)
(1)+(2)=2x+z=27 (4)
(1)+(3)=3x+2z=44(5)
(5)-2*(4)=-x=-10得出x=10
代入(2)得y=9
代入(1)得z=7