To **evaluate** a rational expression
at a particular value of each variable,
evaluate the numerator and denominator and divide the results.
The rational expression its **undefined**
whenever the bottom evaluates to 0.

A rational expression is **simplified**
if

- the top and bottom have only integer coefficients,
- the leading coefficient on the bottom is positive,
- the coefficients have no common factor greater than 1, and
- the top and bottom have no common factor that is not constant.

We add, subtract, multiply, and divide rational expressions using the same techniques as for rational numbers.

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This web page was written in 2010 and 2011 by Toby Bartels, last edited on 2011 October 17. Toby reserves no legal rights to it.

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