Réponse :
Explications étape par étape
a = 1/2, b = -2/3 et c = 5/4
A= a+b+c
A = 1/2 -2/3 + 5/4
= 6/12 -8/12 + 15/12
= -2/12 + 15/12
= 13/15
B = a-b-c
= 1/2 +2/3 - 5/4
= 6/12 + 8/12 - 15/12
= 14/12 - 15/12
= -1/12
C = a-(b-c)
= a - b + C
= 1/2 +2/3 +5/4
= 6/12 + 8/12 + 15/12
= 14/12 + 15/12
= 29/12