Let $X \in \text{Random}(\mathbb{R})$ be a D3161: Random real number such that

(i)	\begin{equation} \mathbb{E} |X|^2 < \infty \end{equation}

Then \begin{equation} \mathbb{E}[(X - \mathbb{E} X)^2] = \mathbb{E}(X^2) - (\mathbb{E} X)^2 \end{equation}