In earlier grades we learned how to do things like apply the distributive property and combine like terms to rewrite expressions in different ways. For example, . The new algebraic expression on the right comes from writing the original on the left in a different way. More precisely, the expression on the left has the same value for all possible inputs as the expression on the right, making them equivalent expressions. This is an example of an identity.

Two examples of identities seen in earlier grades are:

For all possible values of and , the left and right sides of these equations are equal. In fact, the first of these identities can be extended to show that for any positive integer value of the expression

is equivalent to