I am used to expand functions in powers (not neccesarily integer) of an small parameter [tex]\epsilon[/tex](adsbygoogle = window.adsbygoogle || []).push({});

But someone tell me how the log or tan terms are calculated here?

[tex] sech^{-1}\epsilon\sim log(2/\epsilon)-1/4\epsilon^2-....[/tex]

[tex] sin (2\epsilon)\sim 2tan\epsilon -2tan^3\epsilon+...[/tex]

Thanx.

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# Asymptotic expansion

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