Bonjour !
B = (4x-3)(x+2) - (20x-15) = (4x-3)(x+2) - (5*4x-5*3) = (4x-3)(x+2) - 5(4x-3) = (4x-3)(x+2 - 5) =
(4x-3)(x-3)
C = (x²-16) + (x-4)(5x+7)
Identité remarquable : a²-b² = (a-b)(a+b)
C = (x-4)(x+4) + (x-4)(5x+7) = (x-4)(x+4 + 5x+7) = (x-4)(6x+11)
D = (3x-8)(x-7) + (x²-49) = (3x-8)(x-7) + (x-7)(x+7) = (x-7)(3x-8 + x+7) = (x-7)(4x-1)
Voilà !
