Bonjour,
5x(3-6x)-4x
= 15x - 30x² - 4x
= - 30x² + 11x
(3x-2)(5-4x)-3(7x-2)
= 15x - 12x² - 10 + 8x - 21x + 6
= - 12x² + 15x + 8x - 21x - 10 + 6
= - 12x² + x - 4
5x²- 4 (3-7x)
= 5x² - 12 + 28x
= 5x² + 28x - 12
5( 4x-1)-(2x+3)(-5x-7)
= 20x - 5 - (- 10x² - 14x - 15x - 21)
= 20x - 5 + 10x² + 14x + 15x + 21
= 10x² + 20x + 14x + 15x - 5 + 21
= 10x² + 49x + 16