Variable

In algebra, a variable is usually a letter or other symbol that stands for a number or quantity. Variables are used to represent several mathematical ideas. Some common uses are:

to represent unknowns that do not vary


Example

x + 5 = 8

13 - ? = 4


to represent quantities that vary

Example

The area of any rectangle can be represented by the formula A = l × w.

The area (A) varies as either the length (l) or width (w) of the rectangle varies.


to represent properties

Example

The commutative property of addition can be represented by the equation:

a + b = b + a

For any addends (variables a and b), the order in which they are added does not affect the sum.

3 + 4 = 4 + 3

1 + 7 = 7 + 1


See also algebra.