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Selecting the proper rational fraction
Suppose 
is a rational function; that is, 
and 
are polynomial functions. If the degree of is greater than or equal to the degree of , then by long division, 
where 
is a proper rational fraction; that is, the degree of 
is less than the degree of . A theorem in advanced algebra states that every proper rational function can be expressed as a sum
where 
are rational functions of the form
or 
in which the denominators are factors of . The sum is called the partial fraction decomposition of . The first step is finding the form of the partial fraction decomposition of is to factor completely into linear and irreducible quadratic factors, and then collect all repeated factors so that is expressed as a product of distinct factors of the form
and 
.
From these factors we can determine the form of the partial fraction decomposition using the following two rules:
Linear Factor Rule: For each factor of the form , the partial fraction decomposition contains the following sum of m partial fractions:
where A 1, A 2,..., Am are constants to be determined.
Quadratic Factor Rule: For each factor of the form 
, the partial fraction decomposition contains the following sum of m partial fractions:
where A 1, A 2,..., Am, B 1, B 2, …, Bm are constants to be determined.
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