Bonsoir

f (x) = 2.4 x

A ( 8/6 ) = 2.4 x 8/6 = 19.2/6  donc A ∉ C

B ( - 3/6 ) = 2.4 x  - 3/6 = - 7.2/6  donc B ∉ C

C  ( 1.5 ) = 2.4 x 1.5 =  3.6 donc C ∈ C

D ( - 2.6 ) = 2.4 x - 2.6 = - 6.24 donc D ∉ C

f ( - 5 ) = 2.4 x - 5 = - 12

2.4 x = 9

x =  3.75

abscisse = 3.75