Rational Expressions and Replacements
Rational numbers are quotients of integers. Some examples are
, 
, 
.
The following are called rational expressions or fraction expressions. They are quotients, or ratios, of polynomials:
, 
, 
A rational expression is also a division. For example,
means 3 ÷ 4 and 
means (x-8) ÷ (x+2).
Because rational expressions indicate division, we must be careful to avoid denominators of zero. When a variable is replaced with a number that produces a denominator equal to zero, the rational expression is not defined.