Bonjour,
1)
A = - 1/2 + 5/2 x (1 - 1/2)
A = - 1/2 + 5/2 x (1 x 2 / 1 x 2 - 1/2)
A = - 1/2 + 5/2 x (2/2 - 1/2)
A = - 1/2 + 5/2 x 1/2
A = - 1/2 + 5/4
A = - 1 x 2 / 2 x 2 + 5/4
A = - 2/4 + 5/4
A = 3/4
B = 5/7 : 6/7 - (1/2 - 1)
B = 5/7 x 7/6 - (1/2 - 1 x 2 / 1 x 2)
B = 35/42 - (1/2 - 2/2)
B = 35/42 - (- 1/2)
B = 35/42 + 1/2
B = 35/42 + 1 x 21 / 2 x 21
B = 35/42 + 21/42
B = 56/42
B = 14 x 4 / 14 x 3
B = 4/3
2) A et B sont bien les deux inverses.