Réponse:
A = (2x-1)(3x+4)
= 6x² + 8x - 3x - 4
= 6x² + 5x -4
B = (4x+3)(-x+1)
= -4x² + 4x - 3x + 3
= -4x² + x + 3
C = (2x-7)(-4x-3)
= -8x² - 6x + 28x + 21
= -8x² + 22x + 21
D = 2x + 1 - (3x + 1)(4x-1)
= 2x +1 -[(12x²-3x+4x-1)]
= 2x +1 - 12x² +3x - 4x + 1
= 12x² + x + 2
E = (7x+1)(4x-3) - (2x+9)
=28x² - 21x + 4x - 3 - 2x - 9
= 28x² - 19x -12
F = (3x+1)(2x-1)-(5x+3)(-x+7)
= [6x² - 3x + 2x - 1] - [-5x² + 35x - 3x + 21]
= 6x² - x - 1 + 5x² - 32x - 21
= 11x² - 33x - 22
