Explications étape par étape:
A = 6x[2x(-1)] + (2x1) x (x+3)
= 6x[2x(-1)] + 2 (x+3)
= 6 x (-2) + 2x + 6
= -12 + 2x + 6
A= -6 + 2x
B = (-3x+2)(-x-2) - (x+5)(x-4)
= 3x² + 6x - 2x - 4 - (x² - 4x + 5x -20)
= 3x² + 6x - 2x - 4 - (x² + x + 20)
= 3x² + 6x - 2x - 4 - x² + x + 20
= 2x² + 3x + 16
