Sunday, February 12, 2012

Decompose into partial fractions : (8x + 14) / (x + 1)(x + 5)

Given the fraction (8x+14)/
(x+1)(x+5)


We need to rewrite into the form A/(x+1) +
B/(x+5)


==> (8x+14)/ (x+1)(x+5) = A/(x+1) +
B/(x+5)


We will rewrite with the common
denominator.


==> (8x+14)/(x+1)(x+5) = A(x+5)+
B(x+1)]/ (x+1)(x+5)


Now we will multiply by (x+1)(x+5) so
the denominator cancels.


==> 8x + 14 = A(x+5) +
B(x+1)


==> 8x + 14 = Ax + Bx + 5A +
B


==> 8x + 14 = (A+B)x +
(5A+B)


Now we will compare similar
terms.


==> A+B =
8............(1)


==> 5A+B = 14
........(2)


Now we will solve the
system.


We will subtract (1) from
(2).


==> 4A =
6


==> A = 6/4 =
3/2


==> A = 3/2


But
A+B= 8


==> B = 8- A = 8 - 3/2 =
13/2


==> B = 13/2


Now
we will substitute:


==> A/(x+1) + B(x+5) =
(3/2)/(x+1) +
(13/2)/(x+5)


                                   = 3/2(x+2) 
+ 13/2(x+5)


==> (8x+14)/(x+1)(x+5) =
3/2(x+1)  + 13/2(x+5)

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