Evaluating $\int_{-\infty}^\infty \frac{\sin x}{x-i} dx$ I would like to evaluate the integral
$$\int_{-\infty}^\infty \frac{\sin x}{x-i} dx,$$
which I believe should be equal to $\frac{\pi}{e}$. However, I cannot reproduce this result by hand. My work is as follows: first, we evaluate the indefinite integral.
\begin{align*}
\int \frac{\sin x}{x-i} dx &= \int \frac{\sin(u+i)}{u} du \text{ where }u=x-i \\
&= \int \frac{\sin u \cos i + \cos u \sin i}{u} du \\
&= \mathrm{Si}(u) \cos i + \mathrm{Ci}(u) \sin i \\
&= \mathrm{Si}(x-i) \cosh 1 + i\mathrm{Ci}(x-i) \sinh 1 \\
\end{align*}
Then, we insert the bounds.
\begin{align*}
\int_{-\infty}^\infty \frac{\sin x}{x-i} dx &= \mathrm{Si}(\infty-i) \cosh 1 + i\mathrm{Ci}(\infty-i) \sinh 1 \\
&\phantom{=}-\mathrm{Si}(-\infty-i) \cosh 1 - i\mathrm{Ci}(-\infty-i) \sinh 1 \\
&= \frac{\pi}{2}\cosh 1 + 0 +\frac{\pi}{2} \cosh 1 + \pi \sinh 1 \\
&= \pi (\cosh 1 + \sinh 1) \\
&= \pi e
\end{align*}
I assume I have made some mistake in manipulating the complex sine and cosine integrals, since the result would be correct if $\mathrm{Ci}(-\infty-i)$ were evaluated to $-i \pi$. However, I cannot pinpoint the error.
 A: The mistake is simple--$\mathrm{Ci}$ has a branch cut across the negative real axis, so $\mathrm{Ci}(-\infty - i)$ should indeed evaluate to $-i \pi$ rather than $i \pi$.
A: Write the sin-function as the difference of two exponentials and obtain the corresponding integrals by contour integration. This gives the result:
\begin{eqnarray*}
I &=&\int_{-\infty }^{+\infty }dx\frac{1}{x-i}\sin x=\int_{-\infty
}^{+\infty }dx\frac{1}{x-i}\frac{1}{2i}\left\{ e^{ix}-e^{-ix}\right\}  \\
\int_{-\infty }^{+\infty }dx\frac{1}{x-i}e^{ix} &=&2\pi ie^{-1} \\
\int_{-\infty }^{+\infty }dx\frac{1}{x-i}e^{-ix} &=&0 \\
I &=&\frac{1}{2i}2\pi ie^{-1}=\frac{\pi }{e}
\end{eqnarray*}
A: $\newcommand{\angles}[1]{\left\langle\, #1 \,\right\rangle}
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 \newcommand{\expo}[1]{\,{\rm e}^{#1}\,}
 \newcommand{\half}{{1 \over 2}}
 \newcommand{\ic}{{\rm i}}
 \newcommand{\imp}{\Longrightarrow}
 \newcommand{\Li}[1]{\,{\rm Li}_{#1}}
 \newcommand{\pars}[1]{\left(\, #1 \,\right)}
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\begin{align}
\color{#f00}{\int_{-\infty}^{\infty}{\sin\pars{x} \over x - \ic}\,\dd x} & =
\int_{-\infty}^{\infty}{x\sin\pars{x} \over x^{2} + 1}\,\dd x =
\Im\int_{-\infty}^{\infty}{x\expo{\ic x} \over x^{2} + 1}\,\dd x =
\Im\pars{2\pi\ic\,{\ic\expo{\ic\ic} \over \ic + \ic}} =
\color{#f00}{{\pi \over \expo{}}}
\end{align}
The integration was performed along a semi-circle in the upper half complex plane by using the Residues Theorem.
