Bonsoir,
1)
f(x) = 0,5 (2x + 6) (2 - x)
f(x) = (x + 3) (2 - x)
f(x) = 2x - x² + 6 - 3x
f(x) = -x² - x + 6
-x² - x + 6 = 0
a = -1 ; b = -1 ; c = 6
Calcul du discriminant Δ :
Δ = b² - 4ac
Δ = (-1)² - 4 * (-1) * 6
Δ = 1 + 24
Δ = 25
Δ > 0 donc l'equation admet deux solutions
x1 = (-b - √Δ)/2a = (1 - 5)/-2 = -4/-2 = 4/2 = 2
x2 = (-b + √Δ)/2a = (1 + 5)/-2 = 6/-2 = -6/2 = = -3
2) La courbe coupe l'axe des abscisses en -3 et 2
