C'est l'exercice 57 svp c'est pour demain

A = 5/4 x 7/5 x 4/9
A = 35/20 x 4/9
A = 140/180
A = 20 x 7 / 20 x 9
A = 7/9

B = 12/7 x 7/5 x 5/6
B = 84/35 x 5/6
B = 420/210
B = 210 x 2 / 210 x 1
B = 2

C = 12/25 x 15/16
C = 180/400
C = 20 x 9 / 20 x 20
C = 9/20

D = 4/9 x 3/7 x 21/4
D = 12/63 x 21/4
D = 252/252
D = 252 x 1 / 252 x 1
D = 1