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# Constants

A constant is an element of a formula or group of formulas that does not change value. Some of the most famous constants are represented by letters of the Greek alphabet, but italicized letters of the Latin alphabet are also used. A constant can be literal, in which case its value is stated directly in the formula, or defined, in which case a symbol is assigned the literal value at the beginning.

For example, in the formulas

${\displaystyle \phi ={\frac {1+{\sqrt {5}}}{2}},\ \varphi ={\frac {1-{\sqrt {5}}}{2}}\,}$,

and

${\displaystyle F_{n}={\frac {\phi ^{n}-\varphi ^{n}}{\phi -\varphi }}={\frac {\phi ^{n}-\varphi ^{n}}{\sqrt {5}}}\,}$

the constants ${\displaystyle \phi }$ and ${\displaystyle \varphi }$ are defined in relation to the literal constants 1, 2 and ${\displaystyle {\sqrt {5}}}$ in the first formula. The defined constants are then used in the second formula, raising some of them to a power specified by the variable ${\displaystyle n}$.