d=1/2-7/2*-4/21=
e=22/19*(5/2-2)=
d = -6/2*-4/21 =24/42 = 12/24 = 6/12 =1/6
e = 22/19*(5/2-4/2) = 22/19*1/2 = 22/38 = 11/19
1/2=0,5
7/2=3,5
4/21=0,1904761... (a toi d'arrondir)
22/19=1,1578973(a toi d'arrondir)
(5/5-2)=0,5
