Sigma

Ρρ$⟵$ 18 $⟶$Ττ

Pronunciation

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Noun

sigma

1. Eighteen letter of Greek.
2. Σσ, and in the word last position, writes as ς.
3. Standard deviation,has formula $:=\sigma =\sqrt{\frac{1}{n}\sum _{\iota =1}^n(a_{\iota }-\overline{x}{)}^2}$ the average symbol $\overline{x}$ often writes as μ