Bonsoir,
A:4/3-(1/2+7/8)
A = 4 x 8 / 3 x 8 - (1 x 12 / 2 x 12 + 7 x 3 / 8 x 3)
A = 32/24 - (12/24 + 21/24)
A = 32/24 - 33/24
A = - 1/24
B: 4/3-7/5-(3/5-5/7)
B = 4 x 35 / 3 x 35 - 7 x 21 / 5 x 21 - (3 x 21 / 5 x 21 - 5 x 15 / 7 x 15)
B = 140/105 - 147/105 - (63/105 - 75/105)
B = 140/105 - 147/105 - (- 12/105)
B = 140/105 - 147/105 + 12/105
B = 162/105 - 147/105
B = 15/105
B = 15 x 1 / 15 x 7
B = 1/7