$$\text { For a discrete random variable, } \sigma _ { x } = \sum _ { x \text { values } } \left( x - \mu _ { x } \right) \cdot p ( x )$$

$$\text { For a discrete random variable, } \sigma _ { x } = \sum _ { x \text { values } } \left( x - \mu _ { x } \right) \cdot p ( x )$$