Bonjour,
1) C = (a + b)(a - b) = a² - b²
2) E = (2x - 1)(3x + 4) + (5 + x)(2x - 1)
E = (2x - 1)(3x + 4 + 5 + x)
E = (2x - 1)(4x + 9)
F = (4x - 3)(2x + 1) - 5x(4x - 3)
F = (4x - 3)(2x + 1 - 5x)
F = (4x - 3)(-3x + 1)
G = 15x² + 41x + 28
G = (3x + 4)(5x + 7)
H = x² - 25
H = (x)² - 5²
H = (x + 5)(x - 5)
I = 9x² - 16
I = (3x)² - 4²
I = (3x + 4)(3x - 4)