Réponse:
Salut!
Explications étape par étape:
1) f(x) = (8x+5) (5x+8)
2) (8x+5) (5x+8)
40x^2 + 64x + 25x +40
40x^2 +89x +40
3) (8x+5) (5x+8) = 0
A × B = 0
A= 0 ou B = 0
8x+5 = 0 5x+8 =0
8x = -5 5x = -8
8x/8 = -5/8 5x/5 = -8/5
x = -5/8 ou -0,625 x = -1,6