Répondre :
3/4-1/5=15/20-4/20=11/20
1/2-3/7=7/14-6/14=1/14
11/20:1/14=11/20*14=77/10
1/2-3/7=7/14-6/14=1/14
11/20:1/14=11/20*14=77/10
A = ((3/4) - (1/5)) / ((1/2) - (3/7))
A = ((15/20) - (4/20)) / ((7/14) - (6/14))
A = (11/20) / (1/14)
A = (11/20) * (14/1)
A = 154/20
A = 77/10
voilà :)