Diketahui sistem persamaan linear

2x + y + 3z = – 5
2x + 6y – 4z = 48
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– 5y + 7z = – 53 ………………..(1)

3x – 2y + z = – 11
3x + 9y – 6z = 72
_______________-
– 11 y + 7z = – 83 ………………(2)

eliminasi (1) dan (2) :
– 5y + 7z = – 53
– 11y + 7z = – 83
_______________-
6y = 30
y = 5

substitusi :
– 5 (5) + 7z = – 53
– 25 + 7z = – 53
7z = – 28
z = – 4

substitusi :
x + 3(5) – 2( – 4) = 24
x + 15 + 8 = 24
x = 1

x + y + z = 1 + 5 + ( – 4) = 2