Répondre :
bonsoir
f ( - 5 ) = - 5 et f ( 3 ) = - 3
( - 3 + 5 ) / ( 3 + 5 ) = 2 /8 = 1 /4
ax = x /4
f ( - 5 ) = - 5
- 5 * 1/4 + b = - 5
- 5 /4 + b = - 5
b = - 20/4 + 5/4 = - 15/4
f (x) = x /4 - 15/4
d'où f ( 3 ) = 3 * 1/4 - 15/4 = 3/4 - 15/4 = - 12 /4 = - 3