Sunday, August 12, 2012

Can (-12x^2 + 33x - 6)/(x^3 - 4x) be presented as a sum of elementary fractions?

We have to write (-12x^2 + 33x - 6)/(x^3 - 4x) as the sum
of elementary fractions.


(-12x^2 + 33x - 6)/(x^3 -
4x)


=> (-12x^2 + 33x - 6)/x(x^2 -
4)


=> (-12x^2 + 33x - 6)/x(x - 2)(x +
2)


Let this be equal to A/x + B/(x - 2) + C/(x +
2)


=> [A(x^2 - 4) + B(x^2 + 2x) + C(x^2 - 2x)]/x(x^2
- 4) = (-12x^2 + 33x - 6)/(x^3 - 4x)


=> A(x^2 - 4) +
B(x^2 + 2x) + C(x^2 - 2x) = (-12x^2 + 33x - 6)


=>
Ax^2 - 4A + Bx^2 + 2Bx + Cx^2 - 2Cx = -12x^2 + 33x -
6


=> A + B + C = -12, 2B - 2C = 33 and -4A =
-6


=> A = 6/4 = 3/2


B +
C = -13.5 and B - C = 16.5


Add the two 2B =
3


B = 1.5


C =
-15


The given fraction can be written as
1.5/x + 1.5/(x - 2) - 15/(x + 2)

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