{2x-y+3z=21(1)
x+2y-z=3 (2)
3x+2y-2z=9(3)
(1)*2+(2)得
5x+5z=45
x+z=9
(3)-(2)得
2x-z=6
所以
x=5,z=4
从而
y=1
即
{x=5
{y=1
{z=4