Xi

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[[Image:Greek alphabet {{{letter|alpha-omega}}}.png| 200px|center]]
Greek alphabet
Α α Alpha	Β β Beta
Γ γ Gamma	Δ δ Delta
Ε ε Epsilon	Ζ ζ Zeta
Η η Eta	Θ θ Theta
Ι ι Iota	Κ κ Kappa
Λ λ Lambda	Μ μ Mu
Ν ν Nu	Ξ ξ Xi
Ο ο Omicron	Π π Pi
Ρ ρ Rho	Σ σ ς Sigma
Τ τ Tau	Υ υ Upsilon
Φ φ Phi	Χ χ Chi
Ψ ψ Psi	Ω ω Omega
obsolete letters
Image:Greek alphabet digamma2.png Digamma	Image:Greek alphabet san.png San
Image:Greek alphabet qoppa.png Qoppa	Image:Greek alphabet sampi.png Sampi
Image:Greek alphabet stigma.png Stigma	Image:Greek alphabet sho.png Sho

Xi (upper case Ξ, lower case ξ) is the 14th letter of the Greek alphabet. It is pronounced zeye by English speakers, but ksee by modern Greeks. In the system of Greek numerals it has a value of 60.

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

The upper-case letter Ξ is used as symbol for:

• The 'cascade particles' in particle physics.

Xi was also adopted into the early Cyrillic alphabet, as the letter ksi (Ѯ, ѯ).

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Also, XI or xi (both upper or lower case, not a mixture) is the Roman numeral for 11.als:Ξ bg:Кси da:Xi (bogstav) de:Xi el:Ξι es:Ξ fr:Xi gl:Xi ko:Ξ he:קסי nl:Xi nds:Xi ja:Ξ pl:Ksi pt:Ξ sv:Xi zh:Ξ