Bonjour,
a. 5x (3 - 6x) - 4x
= 15x - 30x² - 4x
= - 30x² + 11x
b. (3x - 2) (5 - 4x) - 3 (7x - 2)
= 15x - 12x² - 10 + 8x - 21x + 6
= - 12x² + 2x - 4
c. 5x² - 4 (3 - 7x)
= 5x² - 12 + 28x
= 5x² + 28x - 12
d. 5 (4x - 1) - (2x + 3) (- 5x - 7)
= 20x - 5 - (- 10x² + 14x - 15x - 21)
= 20x - 5 + 10x² - 14x + 15x + 21
= 10x² + 21x + 16.
