^--^ =: A 4- D (^ 4- j) + E (a: +>')•, quae dif- 

 ferentiata dat 



jiydJ/_ tVV (dx — dy) 



(x — yy X — yP 



D ((ix-{-dj) - 2 E (x -i-y) {dx-{- dy) — o. 



%. $. Quo nunc calculus planior reddatur, feorfim 

 partes vel per dx vel pcr dy afFecflas inueftigemus. Pro 

 elemento igitur d x., ii y vt conftans fpedetur, erit 



» yx ' 

 vnde lingulae partes ita fe habebunt: 



-/' iod-S-^ - ,^^ - D - . E (* +^)) 



vbi notetur effe V — V X -}- V Y, hincque 



vvyx--(x-HY)yx-f-2xyY 



vnde hic duplicis generis termini occurrunt, dum vel per 

 y X vel per y Y funt afFedi. Duo autem termini adfimt 

 yY affedi, qui funt 



4XVY , XWY 



qui ergo iundim fumti dabunt 



^. {X' (^-^)-4X), 



quae forma ob 



X=iA + BA:-4-Cxjr + DA-' + E^% hincquc 

 X'z=:B-|-2 C^-f-3 D.vjr-f-4 E a:% dabit 

 X' (jf -j) - + X = - 4 A - B (3 Jf + j) 

 - 2 C [xx -\- xy) - D (jf* + 3 :c xy) -^'B.x^y 



Termini autem per V x affedi funt 



(i^ (^' (^ -^) - ^ (^+^) -^ (^ --^)' " ^ ^ ("^ '^•^) (''"'^^'^- 



Cum 



