Répondre :
tu as vu en cours que
k x (a + b) = k x a + k x b
tu appliques
5 x (a + 9) = 5 x a + 5 x 9 = 5a + 45
et
5 x (6 - b) = 5 x 6 + 5 x (-b) = 30 - 5b
et
5x * (x - 2) = 5x*x + 5x*(-2) = 5x² - 10x.. (* = multiplié par)
tu as vu en cours que
k x (a + b) = k x a + k x b
tu appliques
5 x (a + 9) = 5 x a + 5 x 9 = 5a + 45
et
5 x (6 - b) = 5 x 6 + 5 x (-b) = 30 - 5b
et
5x * (x - 2) = 5x*x + 5x*(-2) = 5x² - 10x.. (* = multiplié par)