bonjour,vous m aider pour mon DM svp

a = 1/28 -1/14+3/28-1/7-5/28+3/4-1/4
a = 1/28+3/28-5/28 -1/14-1/7+3/4-1/4
a = -1/28 -1/14-1/7 +2/4
a = -1/28 -2/28+24/28
a = 21/28
a =3/4

b = -2/3 x  -2.2/25 x-45/ -1.1
b=  -2x -2.2x -45 / 3x25x1.1
b= -2 x-2.2 x-9x5 / 3x5x5x1.1
b = 4.4 x-9 / 15x1.1
b = -39.6 / 16.5
b = - 396 /165

c = 2/3 -5/3(1-1/5)
c = 2/3 -5/3(5/5-1/5)
c=  2/3 -5/3(4/5)
c =  2/3 -4/3
c= -2/3