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partial fract
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2022-08-26
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PARTIAL FRACTIONS
There is a theorem in algebra which
states that a rational expression,
that is, the quotient of two polyno-
mials can be expressed as the sum of
simpler rational expressions depending
on the factorization of the
denominator of the expression.
In Algebra 1 we learn how to add two
rational expressions. For instance,
2
2 2X + 2 4X + 2X
----- + ---------- = ----------
2 3
X-1 X + X + 1 X - 1
is an easy addition after finding the
common denominator. What doesn't seem
so easy is the reverse process. That
is, starting with a sum can we break
it into 'smaller' summands? In other
words if we start with the expression
2
4X +2X
------
3
X -1
is there a systematic way to find the
two summands given above?
The answer is yes. The theorem
deals with what are known as partial
fractions. I won't state the theorem
here, as it requires some explanation
in its most general form. You'll find
a good version of it in Birkoff and
MacLane's A SURVEY OF MODERN ALGEBRA,
or nearly any other book on abstract
algebra. For that matter, since
partial fraction decomposition is used
in integration techniques, you'll find
it described in every calculus text.
As an application of our polynomial
division program, find simpler
summands which add to
3
3X - 7
-------
2 2
(X -X+1)
3
First express 3X -7 as a polynomial
2
in powers of X -X+1. This can be done
by the successive divisions method
used in the TAYLOR's THEOREM article
in this issue. In this particular
case, there is only one division
necessary.
3 2
3X -7 = (3X+3)(X -X+1) - 10
2 2
Now divide both sides by (X -X+1)
3
3X -7 3X+3 10
-------- = -------- - -------
2 2 2 2 2
(X -X+1) X -X+1 (X -X+1)
That's it.
Press "\" to run the LOADSTAR POLYDIV
\oad "loadstar polydiv",8
program now.
Al Vekovius
--------------------------------------