Bonjour '
x = 5/6
y= -1/2
z= -7/12
A = x+y+z
Dénominateur commun pour les trois opérations est 12 :
A = 5/6+(-1/2)+(-7/12)
A = 10/12-6/12-7/12 = -3/12= -1/4
B = x-y+z
B = 5/6-(-1/2)+(-7/12)
B = 10/12+6/12-7/12= 9/12 = 3/4
C = x-(y+z)
C = 5/6- (-1/2+-7/12)
C = 10/12-(-6/12-7/12)
C = 10/12-(-13/12)
C = 10/12+13/12 = 23/12
Bon courage.