Write the solution set of the given homogeneous system in parametric vector form.
2x1 + 2x2 + 4x3 = 0
-4x1 - 4x2 - 8x3 = 0
-6x2 – 6x3 = 0
where the solution set is x=[x1 x2 x3]
x=x3
(Type an integer or simplified fraction for each matrix element.)