Réponse :
Bonjour
f ( 123 ) = 537.6 et f ( 258) = 969.6
( 969.6 - 537.6) / ( 258 - 123) = 432/135 = 3.2
ax = 3.2 x
f ( 123) = 537.6
123 * 3.2 + b = 537.6
393.6 + b = 537.6
b = 537.6 - 393.6
b = 144
f (x) = 3.2 x + 144
donc abonnement = 144 €
f ( 100) = 320 + 144 = 464 €
3.2 x + 144 = 800
3.2 x = 800 - 144
3.2 x = 656
x = 205
800 € correspond à 205 m ³
