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Exercice 1
1)
A = 2/5 - 4/3 + 7/2
A = 12/30 - 40/30 + 105/30
A = 28/30 + 105/30
A = 133/30

B = 2/3 - 5/3 x 3/2
B = 2/3 - 15/6
B = 6/6 - 15/6
B = -9/6
B = -3/2

C = (-7/4 + 1/2) : (2/7 + 1/4)
C =(-7/4 + 2/4) : (4/14 + 1/14)
C = -5/4 : 5/14
C = -5/4 x 14/5
C = -70/20
C = -7/2

D = +28/5 / -21
D = 28/5 : -21
D = 28/5 x -1/21
D = -28/105
D = 7 x -4 / 7 x 5
D = -4/5

2)
a) Inverse de A = -133/30
b) Inverse de B = 3/2

3)
a) A - B
133/30 - 3/2
= 11/30 - 45/30
= 34/30
= 17/15

b) B x C
-3/2 x -7/2
= 21/4

c) A : B
133/30 : -3/2
= 133/30 x -2/3
= -266/90
= -133/45