Variance

Definition

The Variance of RV $X\sim f$ is defined as

$$\text{Var}(X)=\mathbb{E}\left[(X-\mathbb{E}\left[X\right]{)}^2\right]=\mathbb{E}\left[X^2\right]-{\left(\mathbb{E}\left[X\right]\right)}^2$$

by using the Expectation.