2. a. bénéfice = recettes - coût de production donc
B(x)= 3x - (x²-8x+18) = 3x-x²+8x-18 = -x²+11x-18
b. -(x-(11/2))² + (49/4) = - (x²-(22/2)x+(121/4)) + (49/4) = - (x²-11x+(121/4)) + (49/4) = -x²+11x-(121/4)+(49/4) = -x²+11x-18 = B(x)
c. factorisation de B
-(x-(11/2))² + (49/4)