Bonsoir
a) 12 -3 +7 -3 -4 +2 = 21 -10 = 11
b) (6-2) x 5 = 4 x 5 = 20
c) 9 - (4-7) = 9 - (-3)= 9+3 = 12
a = -7.4 et b = +3.5
opposé de a = 7.4 et opposé de b = - 3.5
A = a + b = -7.4 + 3.5 = - 3.9
B = a - b = -7.4 -3.5 = - 10.9
C = -a +b = 7.4 +3.5 = 10.9
D = -a-b = 7.4 -3.5 = 3.9