Adding and Subtracting Rational Expressions
Adding and subtracting Fractions in General
Adding fractions requires a common denominator.
Fractions
We must find something that is common between the fractions.
Example 1, the lowest common denominator was 8 (the lowest number
they both share in common with each other). Example 2, the lowest
number they shared in common was 18, or their product. In either
case, one must do some work with both, the numerator,
denominator, or both fractions. Each case is different.
Addition and subtraction with rational expression
the two fractions share an “a” and a “b”
in common. However, they are in different quantities. Must get
them in the same quantities, by multiplication! Must remember to
multiply the top and bottom!
Factoring -1 from a denominator
Simplify ; 
· The denominators of both are similar. The only difference
they have signs which are reversed.
· We can factor out a -1 from the 213 nd denominator
· by doing so we change the sign in between the expressions
· hence we are left with 
