Calculating probability for collision

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Image Taken from Birthday Paradox

Taken from Birthday Paradox

Why when k$<<$m, we can replace (1-$\frac{i}{m}$) with $e^\frac{i}{m}$? I do not understand the calculation steps in the article starting from the seconds step. Can someone explain to me or point out some of the keywords or topics I should explore to find out?

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We use the taylor serie of $e^x$ (here $x=-\frac{i}{m}$) to the first order:

\begin{equation} e^{-\frac{i}{m}}=1-\frac{i}{m} \end{equation}

with $i\ll m$