Réponse :

Explications étape par étape :

a) 1/2=1x5/2x5 + 7x2/5x2

= 5/10+14/10

= 19/10

b) 8/7=8x12/7x12 - 2x7/12x7

= 96/84 - 14/84

=82/84

c) 2x10/23x10 - 11x23/10x23

= 20/230 - 253/230

= -233/230

d)-3/4=3x9/4x9 -  7x4/9x4

= -27/36 - 28/36

= -55/36