Réponse :
1) B(x) = 120x-(2x²+10x+900)=
120x-x²-10x-900 =
-2x²+110x-900
(-2x+20)(x-45) = -2x²+90x+20x-900 = -2x²+110x-900
2) -2x²+110x-900>0
on calcule delta
b²+4ac=110²-4(-2*-900) = 12100-7200 = 4900
Δ>0; 2solutions
√4900=70
(-b-√Δ)/2a =(-110-70)/-4 =45
(-b+√Δ)/2a = (-110+70)/-4 = 10
x doit etre [10;45]
Explications étape par étape
