Delta (letter)

Delta ('dɛltə; uppercase Δ, lowercase δ; δέλτα, délta, ˈðelta) 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 𐤃. Letters that come from delta include Latin D and Cyrillic Д. A river delta (originally, the delta of the Nile River) is so named because its shape approximates the triangular uppercase letter delta. Contrary to a popular legend, this use of the word delta was not coined by Herodotus. In Ancient Greek, delta represented a voiced dental plosive d. In Modern Greek, it represents a voiced dental fricative ð, like the "th" in "that" or "this" (while d in foreign words is instead commonly transcribed as ντ). Delta is romanized as d or dh. The uppercase letter Δ is used to denote: Change of any changeable quantity, in mathematics and the sciences (more specifically, the difference operator); for example, in the average change of y per unit x (i.e. the change of y over the change of x). Delta is the initial letter of the Greek word διαφορά diaphorá, "difference". (The small Latin letter d is used in much the same way for the notation of derivatives and differentials, which also describe change by infinitesimal amounts.) The Laplace operator: The discriminant of a polynomial equation, especially the quadratic equation: The area of a triangle The symmetric difference of two sets. A macroscopic change in the value of a variable in mathematics or science. Uncertainty in a physical variable as seen in the uncertainty principle. An interval of possible values for a given quantity. 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. A simplex, simplicial complex, or convex hull. In chemistry, the addition of heat in a reaction. In legal shorthand, it represents a defendant.