Bonjour, j'ai un exercice de maths a faire pouvez-vous m'aider svp calculer sous la forme de fraction irréductible A=(3/7-8/21)x(7/12-3/18) B=3/5-7/5:4/9x15 C=-

Bonjour,

Calculer sous la forme de fraction irréductible  :

A=(3/7-8/21)x(7/12-3/18)

A = [(3 x 3) / (7 x 3) - 8/21] x [(7 x 3) / (12 x 3) - (3 x 2) / (18 x 2)]

A = (9/21 - 8/21) x (21/36 - 6/36)

A = 1/21 x 15/36

A = 15/756

A = (3 x 5) / (3 x 252)

A = 5/252

B=3/5-7/5:4/9x15

B = 3/5 - 7/5 x 9/4 x 15

B = 3/5 - 63/20 x 15

B = 3/5 - 945/20

B = (3 x 4) / (5 x 4) - 945/20

B = 12/20 - 945/20

B = - 933/20

C=-2/5+5/2x8/25:7/10

C = - 2/5 + 40/50 x 10/7

C = - 2/5 + 400/350

C = - 2/5 + (50 x 8) / (50 x 7)

C = - 2/5 + 8/7

C = (- 2 x 7) / (5 x 7) + (8 x 5) / (7 x 5)

C = - 14/35 + 40/35

C = 26/35