In mathematics, a formula is generally a rule, principle, or fact that is displayed in terms of mathematical symbols. (Although the Latin plural form of formula is “formulae,” “formulas” is the accepted common use in mathematics.) These equations express a definite, fixed relationship between certain quantities (usually expressed by letters), with their relationship indicated by algebraic symbols. For example, scientist Albert Einstein’s famous E = mc^{2} is a formula representing energy (E) equal to mass (m) times the speed of light (c) squared. The word “formula” is also used in logic; it is written as a propositional or sentential formula, or “a formula in propositional calculus is one that uses ‘and,’ ‘or,’ and so on.”