34 J)ott. (Huseppe Murletta [Memoria I.J 



Nella i)riiiia i]>ot«^si invece della (5) si ha la sejiuente egua- 

 f^lianza : 



(5') '-fi [«, (»•, *•,),-, (*■/, k,,), (r^^^ /,-„_^, ; s -h 1) I = 



= (»•/, . 1— ^'/.^i — ■•>■) • <p, h' — 1, (»•, A-,) ,..., (;•„ A-„) , (*•„+, i"„ M ; *•) J -H 



+ (»•/.+. — ^'/,+i — ••>■) • -h \'h i>\ '<<) VI ('•/, ^■/,)? ('"ft+i /••/,+i ; X) ì -+- 



-+- .V (r„+, — /o,_„ — s + 1) . cp, |/( — !,(>•, /,-,) ,..., (>•„ A-J, (>•,,,., Av,^, ; .V — 1) J -I- 

 -+■ k/,^, . -Sfi [« — 1, (/-, A',) ,..., (»•/, A-,,), (r/,^, A-„+i ; .v)J • 



Kella wecoiula ipotesi avremo iuve(;e : 



(5") (?j [«, ('-1 A-,) ,..., [r„ A-,,} , (>•„+, A-„+, ; *• -t- 1) J = 



= (»•/, , 1 — A-/, t. — s) • 'fi I », ('•. A-,) ,.-v ('•/, ^1.) 1 (»■/,+. ^v, ^1 ; «) I + 

 + 'f (»•„,+, — A;,^., — s -+- 1) . (p, |m — 1, (/•, A-,),..., {»•„ A,,), (r/,^, A,,, i; .S — 1) J 4- 



+ ^'/i+i • 9* [« — 1, ^''i ^'i) vv ('■/, /'■/.) » ('■/,+! '^'/i-fi ; «) J • 



5. — Applica xioìii. 



a) Vogliamo calcolare il iimuero (Hnito) f.^[5,(r,r—S),(2,l)'] 

 (Ielle rette comuni ail una forma (|uadratica e ad un'altra d'or- 

 dine )• di aVj^, incidenti un ])iano :: semplice per la prima ed 

 (r — Syplo j)er la secionda. 



Applicand<> la (i) ahlùamo : 



/, [5, (»•, *• — :i] , (2, 1) I = -s, [5, (;•, r - 3), (2, 1 ; 2) J . 



Per la (5") si ha : 

 tp, [5, (r, r-3), (2, 1; 2)J = '^, (4, (r, r-3), (2, 1; 0) | + (p^ |-i, (r, /— 3), (2, 1; 1) J. 



