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pour l'exercice 1 :
A=(4-7)/5 = -3/5
B=(5*3)/(1*3) + 7/3  B=(15+7)/3  = 22/3
C=(-2*3)/(7*3) + 8/21 = (-6+8)/21 = 2/21
D=(-4*5)/(3*5) + (-2*3)/(5*3) = -20/15 + -6/15 = -26/15
E=(5*3)/(6*3) - (10*2)/(9*2) = 15/18 - 20/18 = -5/18
F=(12*(-4))/15 = -48/15 = -16/5
G=((-15)*(-6))/(2*35) = 90/70 = (90/10)/(70/10) = 9/7
H=(7/2)/(-5/6) = (7/2)*(6/-5) = (7*6)/(2*(-5)) = 42/-10 = 21/-5
J=(-5/4)-((3/4)/(7/5)) = (-5/4) - ((3/4)*(5/7)) = (-5/4) - 15/28 = ((-5*7)/4*7) - 15/28 = (-35-15)/28 = -50/28 = -25/14

A = 4/5 - 7/5
A = - 3/5

B =  5 + 7/3
B = 5 x 3 / 1 x 3 + 7/3
B = 15/3 + 7/3
B = 22/3

C = - 2/7 + 8/21
C = - 2 x 3 / 7 x 3 + 8/21
C = - 6/21 + 8/21
C = 2/21

D = - 4/3 + - 2/5
D = - 4/3 - 2/5
D = - 4 x 5 / 3 x 5 - 2 x 3 / 5 x 3
D = - 20/15 - 6/15
D = - 26/15

E = 5/6 - 10/9
E = 5 x 3 / 6 x 3 - 10 x 2 / 9 x 2
E = 15/18 - 20/18
E = - 5/18

F = 12 x - 4/15
F = - 48/15
F = 3 x - 16 / 3 x 5
F = - 16/5

G = - 15/2 x - 6/35
G = 90/70
G = 10 x 9 / 10 x 7
G = 9/7

H = 7/2 : - 5/6
H = 7/2 x - 6/5
H = - 42/10
H = 2 x - 21 / 2 x 5
H = - 21/5

I = - 2/3 x (4 - 1/3)
I = - 2/3 x (4 x 3 / 1 x 3 - 1/3)
I = - 2/3 x (12/3 - 1/3)
I = - 2/3 x 11/3
I = - 22/9

J = - 5/4 - 3/4 : 7/5
J = - 5/4 - 3/4 x 5/7
J = - 5/4 - 15/28
J = - 5 x 7 / 4 x 7 - 15/28
J = - 35/28 - 15/28
J = - 50/28
J = 2 x - 25 / 2 x 1
J = - 25/14

Les deux autres je les ai faits sur un autre poste