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.