bonjour
il suffit de remplacer par les valeurs
a + b = - 2/3 + 4/5 = - 10/15 + 12 /15 = 2 /15
b - c = 4/5 - ( - 3 /4) = 4 /5 + 3/4 = 16/20 + 15 /20 = 31/20
a - b - b = - 2/3 - ( 4/5) - ( 4/5) = - 2 /3 + 4/5 + 4/5 = - 10/15 + 12/15 + 12/15 = 14/15
continue
