Bonsoir
Ce n'est pas le 140 mais le 130 !
1)
A = (3/5 - 1/2) x 5/2
A = [(3 x 2) / (5 x 2) - (1 x 5) (2 x 5)] x 5/2
A = (6/10 - 5/10) x 5/2
A = 1/10 x 5/2
A = 5/20
A = (5 x 1) / (5 x 4)
A = 1/4
B = (3 - 2/3) / (4/3 x 7)
B = [(3 x 3) / (1 x 3) - 2/3] : 28/3
B = (9/3 - 2/3) : 28/3
B = 7/3 : 28/3
B = 7/3 x 3/28
B = 21/84
B = (21 x 1) / (21 x 4)
B = 1/4
A = B
2)
C = 8/3 - 2/3 : 8/7
C = 8/3 - 16/21
C = (8 x 7) / (3 x 7) - 16/21
C = 56/21 - 16/21
C = 30/21
C = (3 x 10) / (3 x 7)
C = 10/7
D = (- 2/5 + 5/2) : (- 3/4 + 1/2)
D = [(- 2 x 2) / (5 x 2) + (5 x 5) / (2 x 5)] : [- 3/4 + (1 x 2) / (2x 2)]
D = (- 4/10 + 25/10) : (- 3/4 + 2/4)
D = 21/10 : (- 1/4)
D = 21/10 x - 4
D = - 84/10
D = (2 x - 42) / (2 x 5)
D = - 42/5.
3) L'inverse de B est 4 et l'opposé de D est 42/5.
4)
B + D = 1/4 - 42/5 = (1 x 5) / (4 x 5) - (42 x 4) / (5 x 4) = 5/20 - 168/20 = - 163/20
C x D = 10/7 x (- 42/5) = - 420/35 = (35 x - 12) / (35 x 1) = - 12
C/B = 10/7 : 1/4 = 10/7 x 4 = 40/7.
