Bonjour,voici mon exercice de maths :/ (Nvx 3ème) Calculer et donner le résultat de chacune des expressions sous la fomr la plus simple. A =(1-1sur7) : 12sur 5

a = ( 1-1/7) : 12/5
= (7/7 -1/7) : 12/5
= 6/7 : 12/5
= 6/7 x 5/12
= 30/84
=15/42 = 5/14

b =(1/4 -1/5) x (7 +37/9)
= ( 5/20 -4/20) x( 63/9 +37/9)
= 1/20 x 100/9
= 100/180 = 10/18 = 5/9

c  je ne la comprend pas

d =3/4 +1/2(2/3-1)
d = 3/4 +1/2 (2/3-3/3)
d = 3/4 +1/2(-1/3)
d = 3/4  -1/6
d = 9/12 -2/12
d = 7/12