1. 2.
5x+2y-z=-7 x-2y-3z=-1
x-2y+2z=0 2x+y+z=6
3y+z=17 x+3y-2z=13

3. 4. x+3y+z=0
x+y+z=6 x+y-z=0
2x-yz+z=3 x-2y-4z=0
3x-z=0