We have
$\frac{1}{(x+4)(x-1)} = \frac{A}{x+4} + \frac{B}{x-1}$
Multiplying both sides by $(x+4)(x-1)$, we get
$1 = A(x-1) + B(x+4)$
If $x=1$, then $1 = 5B$, so $B = \frac{1}{5}$.
If $x=-4$, then $1 = -5A$, so $A = -\frac{1}{5}$.
Therefore,
$\frac{1}{(x+4)(x-1)} =
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