Variable
From Conservapedia
In mathematics, a variable is a value which usually is the subject or part of a function and must be subject to change while not affecting the structure behind the function in which it acts.
For example, if we have a function: f(x,y) = x2 + 3y, then x,y are said to be the variables of the function, f.
Further, f(1,2) = (1)2 + 3(2) = 1 + 6 = 7. We change the variable and thus alter the value of the function.
The set of all variables upon which a function acts is said to be the domain. The set of all values that a function can take due to its domain is called its range.
