On commence bien entendu par les multiplications ensuite les additions (soustractions)
A/
2/3 + (-3)/4 * 1/2 = 2/3 - 3/4 * 1/2 = 2/3 - (3*1)/(3*4) = 2/3 - 1/4 = (2*4)/(3*4) - (1*3)/(4*3)
= 8/12 - 3/12 = 5/12
B/
= 2/3 + 3/4 - 1/2 = 8/12 + 9/12 - 6/12 = 11/12
D/
= - (2*3*1)/(3*4*2) = 1/4
E/
= 1/3 + 3/4 = 4/12+9/12 = 13/12
F/
= 1/2 - (2/3 + 1/2) = 1/2 - 5/6 = 3/6 - 5/6 = -2/6 = -1/3