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Adding and Subtracting Rational Expressions

Adding and subtracting Fractions in General

Adding fractions requires a common denominator.


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

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