Mathematics: Expressions

Terms and Coefficients
Mathematical expressions consist of a combination of one or more values arranged in terms that are added together. As such, an expression could be just a single number, including zero. A variable term is the product of a real number, also called a coefficient, and one or more variables, each of which may be raised to an exponent. Expressions may also include numbers without a variable, called constants or constant terms. The expression , for example, is a single term where the coefficient is the real number 6 and the variable is . Note that if a term is written as simply a variable to some exponent, like , then the coefficient is 1, because .

Linear Expressions
A single variable linear expression is the sum of a single variable term, where the variable has no exponent, and a constant, which may be zero. For instance, the expression   has 2w as the variable term and 7 as the constant term. It is important to realize that terms are separated by addition or subtraction. Since an expression is a sum of terms, expressions such as  can be written as 
to emphasize that the constant term is negative. A real-world example of a single variable linear expression is the perimeter of a square, four times the side length, often expressed: .
In general, a linear expression is the sum of any number of variable terms so long as none of the variables have an exponent. For example,

is a linear expression, but  is not. In the same way, the expression for the perimeter of a general triangle, the sum of the side lengths:
, is considered to be linear, but the expression for the area of a square, the side length squared: , is not.