Réponse :

Explications étape par étape

A =  12 / (-5/7)             (a/b) / (c/d) = a/b * d/c

= 12 * (-7/5)

= -84/5

B =  (3/5) / (5/6)             (a/b) / (c/d) = a/b * d/c

= 3/5 * 6/5

= 18/25

C = 4/(2/3) - (1/4)/2

= 4 * 3/2 - (1/4 * 1/2)

=  6 - 1/8

= (48 - 1 ) / 8

= 47/8

D = ( 5/7 - 1)  / ( 4/9 + 5/3 )    

= ( -2 / 7 )  /  ( 19/9 )

= -2/7 * 9/19

= -18/133

E =  [ -9/14 + 2/7 ] /  [ 2/3 + 1/2 ]

= [ ( -9 + 4 ) / 14 ]  /  [ (4 + 3 ) / 6 ]

=(-5 / 14 ) /  ( 7/ 6 )

= -5 / 14 * 6 / 7

= -5 / 7 * 3 / 7

= - 15/49