Noun

(mathematics) a standard procedure for solving a class of mathematical problems
"he determined the upper bound with Descartes' rule of signs"
"he gave us a general formula for attacking polynomials"

a liquid food for infants

something regarded as a normative example
"the convention of not naming the main character"
"violence is the rule not the exception"
"his formula for impressing visitors"

a representation of a substance using symbols for its constituent elements
 chemical formula 
a conventionalized statement expressing some fundamental principle

directions for making something

a group of symbols that make a mathematical statement