8x+2y+6z=20, 6x-5y-2z=2,5x+3y+7z=13 nilai x+y+z=

8x + 2y + 6z = 20 ...(i)
6x - 5y - 2z = 2 ...(ii)
5x + 3y + 7z = 13 ...(iii)

Dari (i) dan (ii)
8x + 2y + 6z = 20 (x5)
6x - 5y - 2z = 2 (x2)
———————————-
40x + 10y + 30z = 100
12x - 10y - 4z = 4
————————————(+)
52x + 26z = 104
2x + z = 4...(iv)

Dari (i) dan (iii)
8x + 2y + 6z = 20 (x3)
5x + 3y + 7z = 13 (x2)
—————————————
24x + 6y + 18z = 60
10x + 6y + 14z = 26
———————————-(-)
14x + 4z = 34...(v)

Dari (iv) dan (v)
2x + z = 4 (x2)
14x + 4z = 34 (:2)
——————————
4x + 2z = 8
7x + 2z = 17
——————-(-)
-3x = -9
x = -9/-3 = 3

Dari (iv)
2(3) + z = 4
z = 4 - 6
z = -2

Dari (ii)
6(3) - 5y - 2(-2) = 2
18 - 5y + 4 = 2
-5y = 2 - 22
y = -20/-5
y = 4

Dit: x + y + z = 3 + 4 + (-2)
= 5

Maaf yaaa kalau salah, semoga membantu ^_^