In ancient works such as Euclid's Elements, single letters refer to geometric points and shapes. In the 7th century, Brahmagupta used different colours to represent the unknowns in algebraic equations in the See more

Variables are generally denoted by a single letter, most often from the Latin alphabet and less often from the Greek, which may be lowercase or capitalized. The letter may be … See more

• a, b, c, d (sometimes extended to e, f) for parameters or coefficients
• a0, a1, a2, ... for situations where distinct letters are inconvenient See more

• Edwards, Joseph (1892). An Elementary Treatise on the Differential Calculus (2nd ed.). London: MacMillan and Co.
• Foerster, Paul A. (2006). Algebra and Trigonometry: Functions and Applications See more

It is common for variables to play different roles in the same mathematical formula, and names or qualifiers have been introduced to distinguish them. For example, the general See more

• Lambda calculus
• Observable variable
• Physical constant
• See more