bonsoir, pouvez vous m'aider a ces deux exercices

Bonjour,

53)
1) Multiple commun à 5 et 7 = 35 car 5 x 7 = 35

2) 
a. 8/5 - 3/7
= (8 x 7) / (5 x 7) - (3 x 5) / (8 x 5)
= 56/35 - 15/35
= 41/35

b. 8/5 + 3/7
= (8 x 7) / (5 x 7) + (3 x 5) / (7 x 5)
= 56/35 + 21/35
= (7 x 11) / (7 x 5)
= 77/35

54)
a. 2/7 + 4/9
= (2 x 9) / (7 x 9) + (4 x 7) / (9 x 7)
= 18/63 + 28/63
= 46/63

b. 3/8 - 5/3
= (3 x 3) / (8 x 3) - (5 x 8) / (3 x 8)
= 9/24 - 40/24
= - 31/24

c. - 4/5 - 7/9 
= (- 4 x 9) / (5 x 9) - (7 x 5) / (9 x 5)
= - 36/45 - 35/45
= - 71/45

d. 1 + 2/9
= (1 x 9) / (1 x 9) + 2/9
= 9/9 + 2/9
= 11/9

e. 1 - 7/3
= (1 x 3) / (1 x 3) - 7/3
= 3/3 - 7/3
= - 4/3

f. 3 + 3/4
= (3 x 4) / (1 x 4) + 3/4
= 12/4 + 3/4
= 15/4

Bonsoir.
Exercice 53 :
a. Multiple commun = 5 × 7 = 35
b. a = 8/5 - 3/7
8/5 = 56/35
3/7 = 15/35
56/35 - 15/35 = 41/35
b. 8/5 + 3/7
8/5 = 56/35
3/7 = 15/35
56/35 + 15/35 = 71/35
Exercice 54 :
a. 2/7 + 4/9
DC = 7 × 9 = 63
2/7 = 2/7 × 9/9 = 18/63
4/9 = 4/9 × 7/7 = 28/63
18/63 + 28/63 = 46/63
b. 3/8 - 5/3
DC = 3 × 8 = 24
3/8 = 3/8 × 3/3 = 9/24
5/3 = 5/3 × 8/8 = 40/24
9/24 - 40/24 = (-31)/24
c. (-4/5) - 7/9
DC = (-5) × 9 = 45
(-4/5) = (-4/5) × 9/9 = (-36/45)
7/9 = 7/9 × (-5/5) = (-35/45)
(-36/45) - (-35/45) = (-71/45)
d. 1 + 2/9
1 = 1/1 × 9/9 = 9/9
9/9 + 2/9 = 11/9
e. 1 - 7/3
1 = 1/1 × 3/3 = 3/3
3/3 - 7/3 = (-4)/3
f. 3 + 3/4
3 = 3/1 × 4/4 = 12/4
12/4 + 3/4 = 15/4
Bonne soirée ! :)