Réponse :
bonjour
a + b = 2/7 - 3 /7 = - 1/7
a - b = 2/7 + 3/7 = 5 /7
a + b = - 3 + 7/15 = - 15/15 + 7/15 = - 8 /15
a - b = - 3 - 7/15 = - 15/15 - 7/15 = - 22 /15
a + b = 3/10 - 2 /15 = 9/30 - 4/30 = 5 /30 = 1 /6
a - b = 3/10 + 2/15 = 9/30 + 4/30 = 13 /30
Explications étape par étape :