Bonsoir
A = (2x + 3) (5 - x)
A = 10x - 2x² + 15 - 3x
A = - 2x² + 7x + 15
B = 4 - 2x (3x + 5)
B = 4 - 6x² - 10x
B = - 6x² - 10x + 4
C = (- 4x - 6) (2x - 1) + (2x - 3) (8x - 11)
C = - 8x² + 4x - 12x + 6 + 16x² - 22x - 24x + 33
C = - 8x² + 16x² + 4x - 12x - 22x - 24x + 6 + 33
C = 8x² - 56x + 39.