Xi

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Image:Xi uc lc.svg
Greek alphabet
Αα Alpha	Νν Nu
Ββ Beta	Ξξ Xi
Γγ Gamma	Οο Omicron
Δδ Delta	Ππ Pi
Εε Epsilon	Ρρ Rho
Ζζ Zeta	Σσ Sigma
Ηη Eta	Ττ Tau
Θθ Theta	Υυ Upsilon
Ιι Iota	Φφ Phi
Κκ Kappa	Χχ Chi
Λλ Lambda	Ψψ Psi
Μμ Mu	Ωω Omega
Obsolete letters
Ϝϝ Digamma	Ϸϸ Sho
Ϛϛ Stigma	Ϙϙ Qoppa
Ϻϻ San	Ϡϡ Sampi
Greek diacritics

Xi (uppercase Ξ, lowercase ξ) is the 14th letter of the Greek alphabet. It is generally pronounced /ˈsaɪ/ (UK) or /ˈzaɪ/ (US) in English. In the system of Greek numerals, it has a value of 60. Its Latin equivalent is X.

The lower-case letter ξ is used as a symbol for

• random variables;
• extent of reaction (a topic found most often in chemical engineering kinetics);
• eigenvectors;
• a parameter in a generalized Pareto distribution;
• the symmetric function equation of the Riemann zeta function in mathematics, also known as the Riemann Xi function;
• the damping factor in an RLC circuit;
• a universal set in the set theory;
• one of the two different polypeptide chains of the human embryonic hemoglobin types Hb-Portland (ξ₂γ₂) and Hb-Gower I (ξ₂ε₂).
• frequency

The upper-case letter Ξ is used as symbol for

• The 'cascade particles' in particle physics;
• indicating "no change of state" in Z notation.

Xi was also adopted into the early Cyrillic alphabet, as the letter ksi (Ѯ, ѯ).als:Ξ ar:كشي (حرف إغريقي) arc:Ξ br:Xi (lizherenn) bg:Кси ca:Xi cy:Xi da:Xi (bogstav) de:Xi el:Ξι es:Ξ eu:Xi fr:Xi ga:Xí gd:Xi gl:Xi ko:Ξ id:Xi it:Xi (lettera) he:קסי ka:ქსი (ასო) ht:Ξ ku:Xi la:Xi hu:Kszi ms:Xi nl:Xi (letter) ja:Ξ no:Xi nds:Xi pl:Ksi pt:Ξ ru:Кси (буква) sk:Ksí sl:Ksi fi:Ksii sv:Xi th:ไซ (อักษรกรีก) tr:Ξ zh:Ξ