MCQ
The coefficient of $x^{2012}$ in $\frac{1+x}{\left(1+x^2\right)(1-x)}$ is
  • $1$
  • B
    $2011$
  • C
    $2012$
  • D
    $2013$

Answer

Correct option: A.
$1$
a
(a)

We have, $\frac{1+x}{\left(1+x^2\right)} \frac{(1-x)}{}$

$\frac{1+x}{\left(1+x^2\right)(1-x)}=\frac{x}{1+x^2}+\frac{1}{2\left(1+x^2\right)}$

$+\frac{1}{2(1-x)}$

$=x\left(1+x^2\right)^{-1}+\frac{1}{2}\left(1+x^2\right)^{-1}+\frac{1}{2}(1-x)^{-1}$

Coefficient of $x^{2012}$ in

$\left[x\left(1+x^2\right)^{-1}+\frac{1}{2}\left(1+x^2\right)^{-1}+\frac{1}{2}(1-x)^{-1}\right]$ is

$=0+\frac{1}{2}+\frac{1}{2}=1$

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