# Adding & Subtracting Rational Expressions

When adding or subtracting (maybe even both in one expression) rational expressions the key aspect is that they share a common denominator.  A common denominator means that the denominator of the fraction is all the same.

To get to the point where you have  a common denominator for all the fractions in the expression (if you don’t already) follow the following steps:

1. Factor the expression (if need be)

2. Look at the denominators, what must you multiply one or both sides by in order to get a common (Note: you can multiply each fraction by different values).

3. Multiply one or more of the fractions by the value(s) you found in step 3 (be sure to multiply the numerator and denominator of the fraction)

4. Cancel out like terms in the pattern: 3/1 +|- 1/2 +|- 2/ 3

5. Complete the adding/subtracting

6. You will now have your answer, add the non-permissible values (non-permissible values = numbers that the denominator cannot equal because the denominator will then equal 0)

Ex.