3. Let R2x2 denote the space of 2 x 2 matrices. For each of the following, either prove that the given set is a subspace of R2x2 or else prove that it is not. (a) a 0 0 b a, b ER (b) A ER2x2 0 E im(TA) (c) A ER2x 2 E ker(TA) (d) a b c d E R2x2 | ad - bc = 0