Wednesday, July 1, 2015

Write as partial fractions . (5x-4)/(x-2)(x+3)

We'll decompose the fraction into elementary irreducible
fractions:


(5x-4)/(x-2)(x+3) = A/(x-2) +
B/(x+3)


We'll calculate LCD of the 2 fractions from the right
side.


The LCD is the same with the denominator from the left
side.


LCD = (x-2)(x+3)


We'll multiply
both sides by (x-2)(x+3) and the expression will become:


(5x-4) =
A(x+3) + B(x-2)


We'll remove the
brackets:


5x - 4 = Ax + 3A + Bx -
2B


We'll combine like terms form the right
side:


5x - 4 = x(A+B) +
(3A-2B)


Comparing we'll get:


5 =
A+B


-4 = 3A-2B


We'll use the symmetric
property:


A+B = 5 (1)


3A-2B = -4
(2)


We'll multiply (1) by 2:


2A+2B = 10
(3)


We'll add (3) to (2):


2A+2B+3A - 2B
= 10-4


We'll eliminate like terms:


5A =
6


We'll divide by 5:


A =
6/5


We'll substitute A in (1):


A+B =
5


6/5 + B = 5


We'll subtract 6/5 both
sides:


B = 5 - 6/5 => B = (25-6)/5 => B =
19/5


The given fraction written as partial fractions
is: (5x-4)/(x-2)(x+3) = 6/5(x-2) + 19/5(x+3), where
6/5(x-2) and
19/5(x+3) are partial
fractions.

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