
Adding and Subtracting Rational Expressions
When adding or subtracting fractions with common
denominators, we
Example: Perform the operations. Simplify if
possible.
Be careful with subtraction!!
Do homework problems 13 − 43 everyotherodd
What if the fractions do not have a common denominator?
After we stop crying and/or
cursing, we must find the Least Common Denominator (LCD)
The LCD for a set of fractions is the smallest number that
each denominator will
divide into. And, to find the LCD….
Finding the LCD
• Factor each denominator completely.
• Form a product using each factor (from above).
Be sure to use each factor the
greatest number of times it appears in any one factorization. 
Example: Find the LCD for the following (Do not
need to perform the addition)
Do homework problems 57− 65 odd
Example: Perform the operations. Simplify if possible.
Do homework problems 67 − 85 odd (All problems assigned
in Sec 6.3 can now be worked)
