a = 4/3x1/5 = 4/15
b = 3/5 x8/7 = 24/35
c = 2/5 x4/5 = 8/25
d = 9/11 x5/4 = 45/44
e =6 x 4/5 = 24/5
f = 3/2 x7 = 21/2
g = 8/9 x7/3 =56/27
h = 3/10 x20 = 60/10 = 6
regle : -x- = signe +
-x+ = signe -
donc
a =-5/3 x 7/-2 = + 35/6
b = 14 x -3/4 = -42/4 = -21/2
c = -1/3 x 4/-5 x -9/12 = + 4/15 x -9/12 = +4/15 - 3/4 = -3/15 = -1/5
d = 2/ -15 x 15 x -7/12 = -2 x -7/12 = +14/12 = 7/6
4/
1.5/7 x 2/3 = 3/21 = 1/7
b = 1.2/0.5 x 25/9 = 50*1.2 /9 = 60/9 = 20/3
c = 0.2 /3.5 x 0.5/1.1 =0.2/ 7*1.1 = 0.2/7.7
d = 8/ 1.1 x 3.3/8 = 3.3/1.1 = 3