Consider the subspace W of D, given by
W = span (e2X, e2x cos x, e2x sin x).
(a) Find the matrix of D with respect to
B = {e2x, e2x cos x, e2x sin x}.
(b) Compute the derivative of f(x) = 3e2x - e2x cos x + 2e2x sin x indirectly, using Theorem 6.26, and verify that it agrees with f' (x) as computed directly.