The standard deviation is defined as the square root of the variance:
[tex] \displaystyle \text{Variance: } \sigma^2 = \sum_{i=1}^N \dfrac{(x_i-\mu)^2}{N} [/tex]
[tex] \displaystyle \text{Standard deviation: } \sigma = \sqrt{\sum_{i=1}^N \dfrac{(x_i-\mu)^2}{N}} [/tex]
