Bonsoir,
A = (a - 9) (- 2a - 5)
A = - 2a² - 5a + 18a + 45
A = - 2a² + 13a + 45
B = (- 3a - 12) (5a - 1/6)
B = - 15a² + 3/6a - 60a + 12/6
B = - 15a² + 0,5a - 60a + 2
B = - 15a² - 59,5a + 2
C = (- a - 2/3) (3/4 - a)
C = - 3/4a + a² - 6/12 + 2/3a
C = a² - 3/4a + 2/3a - 6/12
C = a² - 9/12a + 8/12a - 6/12
C = a² - 1/12a - 1/6
D = (t + 1/2) (t - 1/2)
D = t² - 1/2t + 1/2t - 1/4
D = t² - 1/4