1. a+2b+c=6. 3a-b+2c=17. 2a+b-c=9 2. x+y+z= 45 x-y = -4 x - z = -17

nomor 2

x+y+z= 45 ....(1)
x-y = -4 .....(2)
x - z = -17 ......(3)

persamaan 1 dan 2
x+y+z=45
x-y+0=-4
----------------- -
2y +z = 49 .....(4)

persamaan 1 dan 3
x+y+z=45
x+0-z=-17
------------------ -
y+2z = 62 .....(5)

persamaan 4 dan 5
2y+z=49 | ×1 | 2y+z=49
y+2z=62 | ×2 | 2y+4z=124
----------------------------- -
-3z = -75
z = 25

• y+2(25)=26
y =12

• x-12=-4
x=8