bonjour, pourriez-vous m'aider s'il vous plait merci en mathématique: ex 67 merci

Bonjour,

A = 2/7 - 3/7 x 14/9

A = 2/7 - 42/63

A = (2 x 9) / (7 x 9) - 42/63

A = 18/63 - 42/63

A =  (21 x 2) / (21 x - 3)

A = - 2/3

B = 7/8 x (2/3 - 1)

B = 7/8 x [2/3 - (1 x 3) / (1 x 3)]

B = 7/8 x (2/3 - 3/3)

B = 7/8 x - 1/3

B = - 7/24

C = 4/5 x 1/4 + 2/5

C = 4/20 + (2 x 4) / (5 x 4)

C = 4/20 + 8/20

C = 12/20

C = (4 x 3) / (4 x 5)

C = 3/5.