(3)x-y-z=-1
3x+5y+7z=11
4x-y+2z=-1
题目错了:(1)5x-3y+z=2 5x+2y-4z=3 -5x+y-z=2
(2)x+y=-2 x+z=13 y+z=1
(3)x-y-z=-1 3x+5y+7z=11 4x-y+2z=-1
5x-3y+z=2① 5x+2y-4z=3② -5x+y-z=2③
①+②:-y-3z=5④
①+③:-2y=4,y=-2,