Question

x+y+z=4
x-y+z=0
x+y+5z=0

Answer 1

x + y + z = 4 (x + z = 4 - y)
x - y + z = 0
x + y + 5z = 0

Substituindo a primeira na segunda:

x + z - y = 0
4 - y - y = 0
-2y = -4
y = 2

x + z = 4 - y
x + z = 4 - 2
x + z = 2
x - 2 = z

x + y + 5z = 0
x + 2 + 5.(x-2) = 0
x + 2 + 5x - 10 = 0
6x = 8
x = 8/6
x = 4/3

z = x - 2
z = 4/3 - 2
z = 4/3 - 6/3
z = -2/3

=)