Bonjour vous pouvez m'aider svp bonne fête ;)

Bonjour,

1)
A = - 5/4 + 7/4
A = 2/4
A = 2 x 1 / 2 x 2
A = 1/2

B = 7/5 - 7/25
B = 7 x 5 / 5 x 5 - 7/25
B = 35/25 - 7/25
B = 28/25

C = 9 - 1/4
C = 9 x 4 / 1 x 4 - 1/4
C = 36/4 - 1/4
C = 35/4

D = 3/7 x 8/3
D = 24/21

E = 1/100 x - 1/10 - 1/100
E = - 1/1000 - 1 x 10 / 100 x 10
E = - 1/1000 - 10/1000
E = - 11/1000

F = 75/60 x 125/855
F = 9375/51300
F = 75 x 125 / 75 x 684
F = 125/684

2)
A = 5a - b + 3c
A = 5 x 1/5 - 13 + 3 x 5/3
A = 5/5 - 13 + 15/3
A = 1 - 13 + 5
A = 6 - 13
A = - 7

C = ab - 4ac
C = 1/5 x 13 - 4 x 1/5 x 5/3
C = 13/5 - 4/5 x 5/3
C = 13/5 - 20/15
C = 13 x 3 / 5 x 3 - 20/15
C = 39/15 - 20/15
C = 19/15