# Variable

### From Conservapedia

In mathematics, a **variable** is a number whose value is not known. In basic arithmetic problems, the variable is typically the answer which the student must find:

Given: 5 + x = 12 Find x.

Since 5 + 7 = 12, the answer is:

x = 7

A variable is 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*) = *x*^{2} + 3*y*, 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.

Sometimes a function can have also a parameter. A parameter is similar to a variable, but is not written like a variable and is thus more similar to a constant. For example, if we a function: *f*(*x*,*y*) = *x*^{2} + *a**y*, then *a* is said to be a parameter. It does not change like the variables x and y, but it can nonetheless take different values. It is important to clearly distinguish the two concepts.

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.