x + y = 1 y + z = 3 z + x = 6 maka x.y.z adalah

x + y = 1 ---> y = 1 - x
y + z = 3
(1-x) + z = 3
z = 3 -1 + x
z = 2 + x ---> z -x = 2

z + x - 6 = z - x - 2
z - z + x + x = - 2 + 6
2x = 4
 x  = 2

x + y = 1
2 + y = 1
y = 1 - 2 = -1

z = 2 + x = 2 + 2 = 4

Jadi, x = 2, y = -1, z = 4
x.y.z = 2.-1.4 = -8