Leonhard Euler · 1748 · Internet Archive
Introductio in analysin infinitorum
All 320 leaves · leaf 215
Transcription
RECURRENTIBUS.
187
CAP. XIII.
Quinta vero $\frac{2+z}{9(1+z+zz)}$ comparata cum forma
$\frac{A+Bpz}{1-2pz.cos.\Phi + ppzz}$ (218) dat $p=1$, $\Phi = \frac{\varpi}{3} = 60^\circ$;
$A = \frac{2}{9}$; & $B = -\frac{1}{9}$, unde oritur terminus generalis
$+ \frac{2 \sin.(n+1)\Phi - \sin.n\Phi}{9 \sin.\Phi} (-1)^n z^n = + \frac{4 \sin.(n+1)\frac{\varpi}{3} - 2 \sin.n\frac{\varpi}{3}}{9 \sqrt{3}} z^n$
$(-1)^n z^n = + \frac{4 \sin.(n+1)\frac{\varpi}{3} - 2 \sin.n\frac{\varpi}{3}}{9 \sqrt{3}} (-1)^n z^n$. Col-
ligantur hae expressiones omnes in unam summam, ac prodibit
Seriei propositae terminus generalis quaesitus $= (\frac{nn}{12} + \frac{n}{2} + \frac{47}{72})z^n \pm \frac{1
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