X -h L ( A, -f- Bi H- C,) (A, -h B2 -h C

<U, par soustraction,

L ^- - ix(L - L ) - -^-^^-^

iy L (A,-f-B,4-C2)(A,-A,)

L' - jj,A,(A,~A,-+-B,-B,4-C,-C:,)' ou

h p. A, ( A, - A^ -I- B, — B, -4- C, — C.) - ( A, -4- B, ^C,)(\,-A,) 1/ ~ jj.Aj(A,— A,4-B, — Bj4-Ci— Cjj

Par suite,

I^ ^ -(;x-T)f;xA,(A,-A,-hB,-B,4-G,-Ca)-(A,-hB,4-Q(-Vi^l. X -hL ~ |A(Ai-f- B,-hC,HA,H- Bj-hCj)