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Chi (Χ, χ) Definition

Chi (Χ, χ) is the 22nd letter of the Greek alphabet, used to represent the ch sound (as in Scottish loch or German Bauch) in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 600. Letters that came from it include the Roman X and Cyrillic Х.

Usage in Mathematics & Science

The uppercase (Χ) & lowercase (χ) Chi are used for:

  • In statistics, the term chi-squared or χ2 has various uses, including the chi-squared distribution, the chi-squared test, and chi-squared target models.

  • In algebraic topology, Chi is used to represent the Euler characteristic of a surface.

  • In neuroanatomy, crossings of peripheral nerves (such as the optic chiasm) are named for the letter Chi because of its Χ-shape.

  • In chemistry, the mole fraction and electronegativity may be denoted by the lowercase χ.

  • In physics, χ denotes electric or magnetic susceptibility.

  • In rhetoric, both chiastic structure (a literary device) and the figure of speech Chiasmus derive from their names from the shape of the letter Chi.

  • In mechanical engineering, chi is used as a symbol for the reduction factor of relevant buckling loads in the EN 1993, a European Standard for the design of steel structures.

  • In graph theory, a lowercase chi is used to represent a graph's chromatic number.

Greek Alphabet

The letters of the Ancient Greek Alphabet, which are frequently utilized in math and science:

Greek Alphabet

Symbol

Letter

Symbol

Letter

Uppercase

Lowercase

Uppercase

Lowercase

Α

α

Alpha

Ν

ν

Nu

Β

β

Beta

Ξ

ξ

Xi

Γ

γ

Gamma

Ο

ο

Omicron

Δ

δ

Delta

Π

π

Pi

Ε

ε

Epsilon

Ρ

ρ

Rho

Ζ

ζ

Zeta

Σ

σ

Sigma

Η

η

Eta

Τ

τ

Tau

Θ

θ

Theta

Υ

υ

Upsilon

Ι

ι

Iota

Φ

φ

Phi

Κ

κ

Kappa

Χ

χ

Chi

Λ

λ

Lambda

Ψ

ψ

Psi

Μ

μ

Mu

Ω

ω

Omega

Related Definitions

Sources

“Chi (Letter).” Wikipedia, Wikimedia Foundation, 6 Apr. 2020, en.wikipedia.org/wiki/Chi_(letter).

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