# Expressions and variables

An algebraic expression comprises both numbers and variables together with at least one arithmetic operation.

Example:

A variable, as we learned in pre-algebra, is a letter that represents unspecified numbers. One may use a variable in the same manner as all other numerals:

To evaluate an algebraic expression you have to substitute each variable with a number and perform the operations included.

Example:

Evaluate the expression when x=5

First we substitute x with 5

And then we calculate the answer

An expression that represents repeated multiplication of the same factor is called a power e.g.

A power can also be written as

Where 5 is called the base and 3 is called the exponent. The exponent corresponds to the number of times the base is used as a factor.

**Videolesson:** Evaluate the expression when x=4
and y=3

**Discovering expressions, equations and functions, Operations in the right order**