perhatikan persamaan persamaan berikut 2x+3y-z=20 3x+2y+z=20 x+4y+2z=15 tentukan nilai 2x+y-3z

2x + 3y - z = 20
3x + 2y + z = 20
------------------------(+)
5x + 5y = 40 ... pers 1

2x + 3y - z = 20 |×2
x + 4y + 2z = 15
maka
4x + 6y - 2z = 40
x + 4y + 2z = 15
--------------------------(+)
5x + 10y = 55 ... pers 2

pers 1 & 2
5x + 5y = 40
5x + 10y = 55
---------------------(-)
- 5y = - 15
y = 3

subtitusi
5x + 5y = 40
5x + 5(3) = 40
5x + 15 = 40
5x = 40 - 15
5x = 25
x = 5

subtitusi
2x + 3y - z = 20
2(5) + 3(3) - z = 20
10 + 9 - z = 20
19 - z = 20
- z = 20 - 19
- z = 1
z = - 1

nilai 2x + y - 3z
= 2(5) + 3 - 3(-1)
= 10 + 3 + 3
= 16