B D zr ^ et C D n r, ita vt defideretur aequatio reUtio- 

 nem inter has fex lineas a^ b , c et p, q, r exprlmens, 

 lam hic confiderentur anguh ADB, A D C, B D C, quo- 

 rum fumma efl: 360", vnde fi dicatur 



coCADBrry, cof.ADCrrp et cof BDC = «, 

 erit "Vtique per §. 5. 



aa'f-p(34-YY— i -H2ot(3y. 

 At vero per Lemma primum erit 



cof. A D B - AD!ih.l^B: ^^^g pp±,j^ 



eodemque modo 



cof. A D C - ii^^^l:^^^, fiue 3zzPP^'-l^\ 

 ac deniqiie 



col. B D C = 5i^^^^^% fiue arliiiir^. 



Ponanuis nunc breuitatis gratia 

 qq-\-rr-aa-A-^ pp + rr-bb-B et pp-\-qq-cc-Ct 

 vt fiat 



quibns valoribus fubftitutis aequatio noftra 



<xa-f-j3j34-Yy— i-f-2a(3Y 

 induet hanc formam : 



AA _, EB _. CC , , ABC 



-\-T~-^7^.-t-\- 



4^,jrr tppj-r * PP11 — ^^ *ppi1fr^ 



quae in ^ p p q q r r duda dat: 



A A /) ;> H- B B ^ ^ -i- C C r r — 4 p p ^ ^ ?• /• H- A B C . 



Tam in hac aequatione loco litterarum A, B, C, va- 

 lores aflumtos ita fubftituamus, vt formulas pp + qq-ipp-i-rr^ 

 qq-^rr iundas feruemus, ac reperietur fequens aequatio: 



pp 



