Question

{2x-y+3z=21 x+2y-z=3 3x+2y-2z=9}

Answer 1

{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