1. Let

U = {(x, y, z) = R³ | x+y=2z = 0 = x - y},

and let

V = span {(1, 0, -1), (3, 1, 2)}.

Determine the dimensions of both U and V, proving your results.
Note that to prove the dimension, you should use the definition, which
means you need to find a basis. It is not enough to just state a basis,
you must explain why it is a basis.