Bonjour,
a) - 1/11 + 6/11 - - 6/11
= - 1/11 + 6/11 + 6/11
= - 1/11 + 12/11
= 11/11
= 1
b) - 5/12 - 9/8
= (- 5 x 2) / (12 x 2) - (9 x 3) / (8 x 3)
= - 10/24 - 27/24
= - 37/24
c) 2 - 3/4
= (2 x 4) / (1 x 4) - 3/4
= 8/4 - 3/4
= 5/4
d) 21/27 - 14/18
= (21 x 2) / (27 x 2) - (14 x 3) / (18 x 3)
= 42/54 - 42/54
= 0
