bonjour
A = ( 3/4 - 2/7 - 2) x 21/4
a = ( 21/28 - 8/28 - 56/28) x 21/4
a = - 43/28 x 21/4
a = - 903/112 = - 129/16
b = - 2/3 + 5/3 x 12/7 - 18 x 7/27
b = - 2/3 + 60/21 - 126/27
b = - 126/189 + 540/189 - 882/189
b = -468/189 = -52/21
c =( 1 + 2/7 + 3/2) : ( 2/3 + 2/11)
c = (14/14 + 4/14 + 21/14) : ( 22/33 + 6/33)
c = 39/14: 28/33
c = 39/14 x 33/28 = 1287/392
je te laisse le d