Read the definition below, and the example, then answer the question. Definition: Let A be an n x n matrix and H a subspace of R". H is invariant under A if AXE H for all x E H. (a) Show 74 = Nul(A) is invariant under Ax. (b) Let u be an eigenvector of A corresponding to the eigenvalue A. Prove that Span {u} is invariant under the matrix transformation x -> Ax