217 



n'.\0\ 



D e m n s t r a t i o. 

 Notctur stallm esse pro numéro lalcrum ii 



et ita pono. Consequenter habebimus 



AB' -h AC= -f- AD- -h AN' =r 4 AO' X A 



BC' -I-- BD' -t- CE' -h BN' rr: 4 AO' x B 



CD' -f- CE' -f- CF' ^ CN' z= 4 AO' x C 



etc. etc. 



.dénotante 

 I A znz sm. \- Sin, f- sin. (- 



sin. 



sin, 



n 

 (n — 2) -TT» 



sm. 



Çn — 3)7r' 



zn sin. h sin. \- sin. ■ \- . 



C Sin. \- sui. f- sin. \- . 



etc. 

 Quod si igilur ad has séries summandas in subsidium vocemus 

 Lemma 2 (J. 5.) erit 



Suppl. {MX Mémoires de tAcad. 



28 



