pour qu'un produit de facteurs soit nul il suffit que l'un des facteurs le soit
a) (x +3) (x -4) = 0 => x +3 = 0 => x = -3 ou x -4 = 0 => x = 4
b) 2x² -5x =0 => x (2x -5) = 0 => x = 0 ou 2x = 5 => x = 5/2
c) (x +1)(x -5) = 0 => x +1= 0 => x = -1 ou x -5 = 0 => x =5
d) 4x² -5 = 2x (3 +2x) => 4x² -5 = 6x +4x² => 4x² -5 -6x -4x² = 0 => -6x -5 = 0 => -6x = 5 => x = -5/6
e) (x +1)(x +2) = 2 => x² +2x +x +2 = 2 => x² +2x +x +2 -2 =0 => x² +3x =0 => x (x +3) = 0 => x =0 ou x +3 = 0 => x =-3
f) (3x -5)² =0 => 3x = 5 => x = 5/3
