Bonjour,

1) C = (6x - 7)² - (2x - 3)²

C = 36x² - 84x + 49 - (4x² - 12x + 9)

C = 36x² - 84x + 49 - 4x² + 12x - 9

C = 36x² - 4x² - 84x + 12x + 49 - 9

C = 32x² - 72x + 40

2) C = (6x - 7)² - (2x - 3)²

C = (6x - 7 - 2x + 3) (6x - 7 + 2x - 3)

C = (4x - 4) (8x - 10)

C = 8 (x - 1) (4x - 5)

3) (4x - 4) (8x - 10) = 0

4x - 4 = 0               ou            8x - 10 = 0

4x = 4                                     8x = 10

x = 4/4                                   x = 10/8

x = 1                                        x = 5/4.