Réponse :
f(x) = 2,5x
1. f(4) = 2,5*4 = 10
f(12) = 2,5*12 = 30
f(-1) = 2,5*(-1) = -2,5
2. On calcule f(x) = -5
2,5x = -5
x = 5/2,5 = 2
On calcule f(x) = 17,5
2,5x = 17,5
x = 17,5/2,5 = 7
On calcule f(x) = -15
2,5x = -15
x = -15/2,5 = -6
j'espère t'avoir aidé !