2 cof. 5 a cof. 5 ^ cof. j tf 

 Tnde fiet 



yfin. J- fin.(j- — o) fiu. Cj- — b) fin. j- — c) 



=i:-2cof.| (A + B-f Cj cofifl cof.l^ cof.^c, 



qno valore fuffedo in expreflione pro tang. BC, Theo- 

 remate praecedente inueda, iiabebimus: 



tang, B C = - tang. \ a ta ng. i b tang.|^ ^ 

 ^ cof. ^ (A 4- B -H C) 



§. 20. Theorema. XV. lisdem pofitis fi Jiatuatur 

 z(A4-B-f-C) = S, ^ff 



Bc — y - t^o^- s 



"ng, _ ^^^. ^5 _^-j ^^j,^ ^^ _ g^ ^.^^j^ ^3 _ g- 



Demonjir. Per ea quae §. 14. demonftrauimus fit 



tang. i a tang. | ^ tang. | <: r: cof. S V—, ,, ~Tl -\ , 



° ° ° cci/.(S — Aj coy.(S-BJco/. {S-CJ> 



vnde h'quet propofitum. Caeterum idem quoque hunc in 

 modum demonftratur. In triangulo redangulo C B F eft 



tang. B C - :^, , 



iam quum fit 



CBF~S-A et B¥ — \a, fiet 



_p_ tang. ~ a _ , — cof S 



""^' "cof.(S-A)"" cof. (S^Jcof. (S-B) cof.(S-C5 

 idiig. a a — ¥ -^Sjjfi^ h) coj. (s - cj • 

 Tum vero quum fit per §. 15. 



A^a Acad. Imp, St;. Tom. VI P,I, K coU 



