Let $\mathcal{P}^{(4)}$ denote the vector space consisting of all polynomials $p(x)$ of degree $\leq 4$.
(a) Are $x^3-3 x+1, x^4-6 x+3, x^4-2 x^3+1$ linearly independent elements of $\mathcal{P}^{(4)}$ ?
(b) What is the dimension of the subspace of $\mathcal{P}^{(4)}$ they span?