Statistics & Probability

$\displaystyle \sum_{i=1}^n (x_i - \bar x)^2 = \displaystyle \sum_{i=1}^n x_i^2 - n \bar x^2$

$s^2 = \displaystyle \sum_{i=1}^n \frac{(x_i - \bar x)^2}{n} = \frac{\displaystyle \sum_{i=1}^n x_i^2}{n} - \bar x^2$

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