-2y=4

y=-2

Substitute into the equation again

5x+z=-4 5x-4z=7

2- 1

-5z= 1 1

z=- 1 1/5

Substitute again

x= 13/25

2-3

x-y= 12

4+ 1

2x= 10

x=5

y=-7

z=8

3、x-y-z=- 1

3x+5y+7z= 1 1

4x-y+2z=- 1

Destroy Yuan. 1. Equation 1-2 gives -5X+5Z=- 1, and equation 1+3 gives -2Y=4, so Y=-2. ..........