complex fraction	A quotient of two fractions.
complex rational expression	A quotient of two rational expressions.
constant of variation	Represented by the variable k in variation problems, the constant of variation is a number that relates the input and the output.
direct variation	A type of variation where the output varies directly with the input. Direct variation is represented by the formula y = kx.
domain	The set of all possible input values for the variable in a function.
excluded value	A value for the variable that is not included in the domain because it would cause the function to be undefined.
extraneous solution	A solution of the simplified form of an equation that does not satisfy the original equation and must be discarded.
greatest common factor	The largest number (or expression) that is a factor of a set of two or more numbers (or expressions).
inverse variation	A type of variation where the output varies inversely with the input. Inverse variation is represented by the formula .
joint variation	A type of variation where the output varies jointly with multiple inputs. Joint variation is represented by the formula y = kxz.
least common denominator	The smallest number (or expression) that is a multiple of all the denominators in a group of fractions (or rational expressions).
least common multiple	The smallest number (or expression) that is a multiple of a set of two or more numbers (or expressions).
prime factorization	The process of breaking down a number (or expression) into its prime multiplicative factors. For example, the prime factorization of 12xy is 2 • 2 • 3 • x • y.
rational equation	An equation that contains one or more rational expressions.
rational expression	A fraction that contains a polynomial as the numerator, denominator, or both.
rational formula	A formula expressed as a rational equation.