Domains of Rational Expressions

Recall that a rational number is a number that can be expressed as a quotient of two integers whose denominator is not equal to zero. Numbers such as $\frac{2}{5},$ $\frac{8}{3},$ 0, and 100 are rational numbers. The definition of rational numbers can be extended to quotients whose numerator and denominator are polynomials.

Rational expressions indicate division; hence, you should be careful when replacing the variable in the denominator with a number. In case the substituted number for the variable of a rational expression makes the denominator equal to zero, the result is said to be undefined. Thus, the said number cannot be a value of the variable in the given rational expression.