For other uses, see Delta. Delta (uppercase Δ, lowercase δ; Greek: Δέλτα [ðelta] Thelta) is the fourth letter of the Greek alphabet. In the system of Greek numerals it has a value of 4. It was derived from the Phoenician letter Dalet  . Letters that arose from Delta include the Latin D and the equivalent in the Cyrillic alphabet: Д.
In Modern Greek it represents a voiced dental fricative /ð/, (like the th in the English word this) but in the Ancient Greek language, it represented a voiced dental plosive /d̪/.
A river delta is named after the letter delta because it has roughly the triangular shape of the upper-case delta.
The upper-case letter Δ can be used to denote:
- Failed to parse (Missing texvc executable; please see math/README to configure.): {y_2-y_1\over x_2-x_1} = {\Delta y \over \Delta x}
= the average change of y per unit x – commonly known as the change of y over the change of x
- By extension of the above, change generally, a use which shows up frequently in medical charts
- The Laplace operator:
- Failed to parse (Missing texvc executable; please see math/README to configure.): \Delta f = \sum_{i=1}^n {\frac{\partial^2 f}{\partial x_i^2}}
- Failed to parse (Missing texvc executable; please see math/README to configure.): \Delta = b^2 - 4ac\,\!
- A macroscopic change in the value of a variable in mathematics or science
- Any of the delta particles in particle physics
- The determinant of the matrix of coefficients of a set of linear equations (see Cramer's Rule)
- That an associated locant number represents the location of a covalent bond in an organic compound, the position of which is variant between isomeric forms
- In legal shorthand, it represents a defendant
- In the financial markets, it is one of the Greeks that describes the rate of change of an option price for a given change in the underlying benchmark
- In genetics, it can stand for a gene deletion, e.g. the CCR5-Δ32 a deletion of the CCR5 at the 32nd bp segment
- In chemistry, it denotes the change in a physical property such as heat, e.g ΔTemp would stand for the change in Temp
The lower-case letter δ can be used to denote:
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