s_x² := $\frac{\mathrm{<span>1</span>}}{\mathrm{<span><var>n</var></span>}}$ Σ (n) (i = 1) (x_i - x (-) )² = $\frac{\mathrm{<span>1</span>}}{\mathrm{<span><var>n</var></span>}}$ Σ (n) (i = 1) x_i² - (x (-) )²