Difference between revisions of "Partial fraction decomposition"
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Any [[rational function]] of the form <math>\frac{P(x)}{Q(x)}</math> maybe written as a sum of simpler rational functions. | Any [[rational function]] of the form <math>\frac{P(x)}{Q(x)}</math> maybe written as a sum of simpler rational functions. | ||
| − | + | To find the decomposition of a rational function, first perform the long division operation on it. This transforms the function into one of the form <math>\frac{P(x)}{Q(x)}=S(x) + \frac{R(x)}{Q(x)}</math>, where <math>R(x)</math> is the remainder term and <math>\deg R(x) \leq \deg Q(x)</math>. | |
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| − | To find the decomposition of a rational function, first perform the long division operation on it. This transforms the function into one of the form <math>\frac{P(x)}{Q(x)}=S(x) + \frac{R(x)}{Q(x)}</math>, where <math>R(x)</math> is the remainder term and <math>deg R(x) \leq deg Q(x)</math>. | ||
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Next, for every factor <math>(a_nx^n+a_{n-1}x^{n-1}+\ldots +a_0)^m</math> in the factorization of <math>Q(x)</math>, introduce the terms | Next, for every factor <math>(a_nx^n+a_{n-1}x^{n-1}+\ldots +a_0)^m</math> in the factorization of <math>Q(x)</math>, introduce the terms | ||
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<math>\frac{A_1x^{n-1}+B_1x^{n-2}+\ldots+Z_1}{a_nx^n+a_{n-1}x^{n-1}+\ldots+a_0}+\frac{A_2x^{n-1}+B_2x^{n-2}+\ldots+Z_2}{(a_nx^n+a_{n-1}x^{n-1}+\ldots+a_0)^2}+\ldots+\frac{A_mx^{n-1}+B_mx^{n-2}+\ldots+Z_m}{(a_nx^n+a_{n-1}x^{n-1}+\ldots+a_0)^m}</math> | <math>\frac{A_1x^{n-1}+B_1x^{n-2}+\ldots+Z_1}{a_nx^n+a_{n-1}x^{n-1}+\ldots+a_0}+\frac{A_2x^{n-1}+B_2x^{n-2}+\ldots+Z_2}{(a_nx^n+a_{n-1}x^{n-1}+\ldots+a_0)^2}+\ldots+\frac{A_mx^{n-1}+B_mx^{n-2}+\ldots+Z_m}{(a_nx^n+a_{n-1}x^{n-1}+\ldots+a_0)^m}</math> | ||
| − | + | (Note that the variable <math>Z_i</math> has no relation to being the 26th letter in the alphabet.) | |
| − | Note that the variable <math>Z_i</math> has no relation to being the 26th letter in the alphabet. | ||
Next, take the sum of every term introduced above and equate it to <math>\frac{R(x)}{Q(x)}</math>, and solve for the variables <math>A_i, B_i, \ldots</math>. Once you solve for all the variables, then you will have the partial fraction decomposition of <math>\frac{R(x)}{Q(x)}</math>. | Next, take the sum of every term introduced above and equate it to <math>\frac{R(x)}{Q(x)}</math>, and solve for the variables <math>A_i, B_i, \ldots</math>. Once you solve for all the variables, then you will have the partial fraction decomposition of <math>\frac{R(x)}{Q(x)}</math>. | ||
Revision as of 21:59, 18 June 2006
Any rational function of the form 
maybe written as a sum of simpler rational functions.
To find the decomposition of a rational function, first perform the long division operation on it. This transforms the function into one of the form 
, where 
is the remainder term and 
.
Next, for every factor 
in the factorization of 
, introduce the terms
(Note that the variable 
has no relation to being the 26th letter in the alphabet.)
Next, take the sum of every term introduced above and equate it to 
, and solve for the variables 
. Once you solve for all the variables, then you will have the partial fraction decomposition of .
Partial fraction decomposition has several common uses. It allows for much easier integration of rational functions, allowing one to integrate a complicated rational function term by term. Additionally, it can be used in summations, causing sums to often telescope or have a much easier form which can be expressed with a closed form. It has several other minor uses, as well.
