Bonjour,
(2x + 5) (3x + 8)
= 2x * 3x + 2x * 8 + 5 * 3x + 5 * 8
= 6x² + 16x + 15x + 40
= 6x² + 31x + 40
(4x + 9)²
= (4x)² + 2 * 4x * 9 + 9²
= 16x² + 72x + 81
(-3x - 4) (-2x + 8)
= -3x * - 2x - 3x * 8 - 4 * 8
= 6x² -24x + 8x -32
= 16x² - 16x - 32
(x - 9)²
= x² - 2 * x * 9 + 9²
= x² - 18x + 81
7x + 3x(2x - 5)
= 7x + 3x * 2x + 3x * (-5)
= 6x² - 8x
13x + (3x - 8)(4x + 5)
= 13x + 3x * 4x + 3x * 5 - 8 * 4x - 8 * 5
= 13x + 12x² + 15x - 32x - 40
= 12x² - 4x - 40
3(x-2) - 5(4-2x)
= 3 * x + 3 * (-2) - 5 * 4 - 5 * 2x
= 3x - 6 - 20 - 10x
= 13x - 26
10x - (4x + 11) (2x-3)
= 10x - 4x * 2x - 4x * -3 - 11 * 2x - 11 * (- 3)
= 10x - 8x² + 12x - 22x + 33
= -8x² + 10x - 10x + 33
= - 8x² + 33