Bonsoir J'ai besoin d'aide pour ces exercices de maths Svp Merci d'avance

3)
A = 3 x a - b - c
A = 3 x 2/3 - - 3/2 - - 3/4
A = 3 x 2/3 + 3/2 + 3/4
A = 6/3 + 3/2 + 3/4
A = 6 x 4 / 3 x 4 + 3 x 6 / 2 x 6 + 3 x 3 / 4 x 3
A = 24/12 + 18/12 + 9/12
A = 51/12
A = 3 x 17 / 3 x 4
A = 17/4

B = - 2 x a + 4 x b - 5 x c
B = - 2 x 2/3 + 4 x - 3/2 - 5 x - 3/4
B = - 4/3 - 12/2 - 15/4
B = - 4 x 4 / 3 x 4 - 12 x 6 / 2 x 6 - 15 x 3 / 4 x 3
B = - 16/12 - 72/12 - 45/12
B = - 133/12

C = 1/a + 1/b + 1/c
C = 1 : 2/3 + 1 : -  3/2 + 1 : - 3/4
C = 1 x 3/2 + 1 x - 2/3 + 1 x - 4/3
C = 3/2 - 2/3 - 4/3
C = 3 x 3 / 2 x 3 - 2 x 2 / 3 x 2 - 4 x 2 / 3 x 2
C = 9/6 - 4/6 - 8/6
C = - 3/6
C = 3 x - 1 / 3 x 2
C = - 1/2

D = a + c
      a - b
D = 2/3 - 3/4
      2/3 + 3/2
D = 2 x 4 / 3 x 4 - 3 x 3 / 4 x 3
      2 x 2 / 3 x 2 + 3 x 3 / 2 x 3
D = 8/12 - 9/12
       4/6 + 9/6
D = - 1/12 : 13/6
D = - 1/12 x 6/13
D = - 6/156
D = 6 x - 1 / 6 x 26
D = - 1/26

4)
A = 3/2 - 1/3
      3/4 + 2/3
A = 3 x 3 / 2 x 3 - 1 x 2 / 3 x 2
      3 x 3 / 4 x 3 + 2 x 4 / 3 x 4
A = 9/6 - 2/6
    9/12 + 8/12
A = 7/6 : 17/12
A = 7/6 x 12/17
A = 84/102
A = 6 x 14 / 6 x 17
A = 14/17

B = 2 + 2/7 : 5/14
B = 2 + 2/7 x 14/5
B = 2 + 28/35
B = 2 x 35 / 1 x 35 + 28/35
B = 70/35 + 28/35
B =  98/35
B = 7 x 14 / 7 x 5
B = 14/5

C = - 3/14 - 3 : 7/5 + 2
C = - 3/14 - 3 x 5/7 + 2
C = - 3/14 - 15/7 + 2
C = - 3/14 - 15 x 2 / 7 x 2 + 2 x 14 / 1 x 14
C = - 3/14 - 30/14 + 28/14
C = - 5/14

D = 7/5 + 8/15 : 2/3 - 19/2
D = 7/5 + 8/15 x 3/2 - 19/2
D = 7/5 + 24/30 - 19/2
D = 7 x 6 / 5 x 6 + 24/30 - 19 x 15 / 2 x 15
D = 42/30 + 24/30 - 285/30
D = - 267/30
D = 3 x - 89 / 3 x 10
D = - 89/10