Salut ! Je dois faire ceci mais je ne comprend pas. Pourriez vous m'aider

Bonsoir,

Exercice 1 :
A = -8/25 x 5/12
A = (-2 x 4 x 5)/(5 x 5 x 4 x 3)
A = -2/(5 x 3)
A = -2/15

B = -9/35 x -15/-27
B = (-9 x (-1) x 3 x 5)/(5 x 7 x (-9) x 3)
B = -1/7

C = 7 x 5/21
C = 7/1 x 5/21
C = 35/21
C = (7 x 5)/(7 x 3)
C = 5/3

D = -16/5 x 25/12 x -9/-10
D = (-4 x 4 x 5 x 5 x (-3) x 3)/(5 x 4 x 3 x 5 x (-2))
D = (-4 x (-3))/-2
D = 12/2 = 6

E = 7/15 - 2/15 x -9/4
E = 7/15 - [(2 x (-3) x 3)/(3 x 5 x 2 x 2)]
E = 7/15 - [-3/(5 x 2)]
E = 7/15 - (-3/10)
E = 7/15 + 3/10
E = (7 x 2)/(15 x 2) + (3 x 3)/(10 x 3)
E = 14/30 + 9/30
E = 23/30

F = (-3/4 + 1/6) x (5/3 - 6/5)
F = ((-3 x 3)/(4 x 3) + (1 x 2)/(6 x 2)) x ((5 x 5)/(3 x 5) - (6 x 3)/(5 x 3))
F = (-9/12 + 2/12) x (25/15 - 18/15)
F = -7/12 x 7/15
F = (-7 x 7)/(12 x 15)
F = -49/180

Exercice 2 :
1 - (1/9 + 5/12)
= 1/1 - ((1 x 4)/(9 x 4) + (5 x 3)/(12 x 3))
= (1 x 36)/(1 x 36) - (4/36 + 15/36)
= 36/36 - 19/36
= 17/36