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
x + 5 = 8
13 - ? = 4
to represent quantities that vary
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
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.