Bonjour je dois faire l excercice N°44 et 45

44)
a) - 4/21 - (- 9/7)
= - 4/21 + 9/7
= - 4/21 + 9 x 3 / 7 x 3
= - 4/21 + 27/21
= 23/21

b) 5/6 - (- 1/7)
= 5/6 + 1/7
= 5 x 7 / 6 x 7 + 1 x 6 / 7 x 6
= 35/42 + 6/42
= 41/42 

c) - 7/6 + 4/9
= - 7 x 3 / 6 x 3 + 4 x 2 / 9 x 2
= - 21/18 + 8/18
= - 13/18

45)
a) 3/8 - x/8 = 7/8
- x = 7 - 3 x = - 4
Donc :
3/8 - (- 4/8) = 7/8

b) 5/3 - x/6 = - 7/6
- x/6 = - 7/6 - 10/6
- x = - 17
x = 17
Donc :
5/3 - 17/6 = - 7/6

c) x/15 + 9/5 = 8/15
x/15 + 27/15 = 8/15
x = 8 - 27
x = - 19
Donc :
- 19/15 + 9/5 = 8/15

d) x/7 + 5/14 = - 1/14
2x/14 + 5/14 = - 1/14
2x = - 1 - 5
x = - 6/2
x = - 3
Donc :
- 3/7 + 5/14 = - 1/14