Can you show it's a subspace?
Assuming that you can, if you want to show that the dimension is at least 2, consider the following two cases :
(1) and are linearly independent : then the subspace contains the span of , which is two dimensional (in fact, try to show that it's equal to the span of );
(2) are linearly dependent : then the space is all of ! (Can you see why?)
Can you generalize to higher dimensions?