In Example BSP4 we showed that \begin{equation*} S=\set{x-2,\,x^2-4x+4,\,x^3-6x^2+12x-8,\,x^4-8x^3+24x^2-32x+16} \end{equation*} is a basis for $W=\setparts{p(x)}{p\in P_4,\ p(2)=0}$. Thus, the dimension of $W$ is four, $\dimension{W}=4$.
Note that $\dimension{P_4}=5$ by Theorem DP, so $W$ is a subspace of dimension 4 within the vector space $P_4$ of dimension 5, illustrating the upcoming Theorem PSSD.