X+2y+3z=8 -x+y+3z=4 2x-y-z=-4

x+2y+3z = 8 ...(1)
-x+y+3z = 4 ...(2)
2x-y-z = -4 ...(3)
eliminasi (1) dan (2)
x+2y+3z = 8
-x+y+3z = 4
___________-
2x+y = 4 ...(4)
eliminasi (2) dan (3)
-x+y+3z = 4 |x1| -x+y+3z = 4
2x-y-z = -4   |x3| 6x-3y-3z = -12
                           ____________+
                            5x-2y = -8 ...(5)
eliminasi (4) dan (5)
2x+y = 4     |x2| 4x+2y = 8
5x+2y = -8  |x1| 5x+2y = -8
                         __________-
                               -x = 16
                                x = -16
subtitusi (4)
2x+y = 4
2(-16)+y = 4
-32+y = 4
y = 4+32
y = 36

subtitusi (1)
x+2y+3z = 8
-16+2(36)+3z = 8
-16+72+3z = 8
56+3z = 8
3z = 8-56
3z = -48
z = -48/3
z = 16

x = -16
y = 36
z = 16