Bonsoir,
C = 2x² + x = x × 2x + x × 1 = x(2x + 1)
F = 6x² - 9x = 3x × 2x - 3x × 3 = 3x(2x - 3)
I = 42x² - 24x = 6x × 7x - 6x × 4 = 6x(7x - 4)