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Sigma

letter in the Greek alphabet

Sigma (uppercase/lowercase Σ σ ς), is the letter of the Greek alphabet, used to represent the "s" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 200. Letters that came from it include the Roman S and Cyrillic С.

Mathematics

Sigma is the short-hand symbol for summation, often used to condense Taylor series equations. Sigma also allows for trigonometric equations such as sine, cosine, and tangent to be written out and solved on paper.