Leonhard Euler · 1748 · Internet Archive
Introductio in analysin infinitorum
All 320 leaves · leaf 243
Transcription
AC DIVISIONE ANGULORUM. 215 CAP. XIV.
& generaliter, si $n = 2m+1$, erit
$n\tan nz = \tan z - \tan(\frac{\pi}{n}-z)+\tan(\frac{\pi}{n}+z)-\tan(\frac{2\pi}{n}-z)+\tan(\frac{2\pi}{n}+z)-\tan(\frac{3\pi}{n}-z)+\dots-\tan(\frac{m\pi}{n}-z)+\tan(\frac{m\pi}{n}+z).$
254. Tum vero productum ex his Tangentibus omnibus erit $= \tan nz$, propterea quod per signorum negativorum numerum alternatim parem & imparem, superior signorum ambiguitas tollitur. Sic erit
$\tan z = \tan z$
$\tan 3z = \tan z \tan(\frac{\pi}{3}-z)\tan(\frac{\pi}{3}+z)$
$\tan 5z = \tan z \tan(\frac{\pi}{5}-z)\tan(\frac{\pi}{5}+z)\tan(\frac{2\pi}{5}-z)\times \tan(\frac{2\pi}{5}+z)$
& generaliter, si $n = 2m+1$, erit
$\tan nz = \tan z \tan(\frac{\pi}{n}-z)\tan(\frac{\pi}{n}+z)\tan(\frac
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