1. A = 8x² + 2x - 7 - (4x+1)(2x-3)
= 8x² + 2x - 7 - (8x² -12x + 2x - 3)
= 8x² + 2x - 7 - 8x² +10x + 3
= 12x - 4
= 4 (3x - 1)
2. A = 0 => 12x - 4 = 0
=> 12x = 4
=> x = 4/12
=> x = 1/3
Ou tu peux utiliser l'équation factorisée :
A = 0 => 4 (3x - 1) = 0
=> (3x - 1) = 0
=> 3x = 1
=> x = 1/3