Bonjour pourriez-vous m’aider svp ex a) 27 et 28, merci

numéro 27      Tu multiplies les numérateurs entre eux, puis les dénominateurs et tu simplifies le résultat.
A = 2 X 3/5= 6/5
B = -5 X 2/9 = -10/9
C = -9/4 X -5/7 X -3/2 = - X- = + puis + X - = -
       + 45/28 X -3/2 = -135/56 
D = -2/11 X 2,4 = -4,8/11

Exercice 28
25/21 x 14/15
350/315 = 70/63 = 
10/9
21/6 X -9/56 = - 189/336= -63/112
18/15 X 75/-16 = -1350/240 = -270/ 48 = -90/16

Bonjour,

A = 2 x 3/5
A = 6/5

B = -5 x 2/9
B = -10/9

C = -9/4 x -5/7 x -3/2
C = -135/56

D = -2/11 x 2,4
D = -48/110
D = -24/55

Exercice 28 :

A = 25/21 x 14/15
A = 25/15 x 14/21
A = (5 x 5)/(5 x 3) x (2 x 7)/(3 x 7)
A = 5/3 x 2/3
A = 10/9

B = 21/-6 x -9/56
B = 21/56 x 9/6
B = (3 x 7)/(8 x 7) x (3 x 3)/(2 x 3)
B = 3/8 x 3/2
B = 9/16

C = -49/63 x -9/-28
C = -(7 x 7)/(9 x 7) x 9/28
C = -7/9 x 9/28
C = -7/28 x 9/9
C = -7/(7 x 4)
C = -1/4

D = 18/15 x 75/-16
D = 75/15 x -18/16
D = (15 x 5)/15 x (-2 x 9)/(2 x 8)
D = 5 x -9/8
D = -45/8