bonjour
f ( 3) = 1 et f ( - 2 ) = - 1
( - 1 - 1 ) / ( - 2 - 3 ) = - 2 / - 5 = 2/5
donc ax = 2 x /5
f ( 3) = 1
3 * 2/5 + b = 1
6/5 + b = 1
b = 1 - 6/5
b = 5/5 - 6 /5 = - 1 /5
f (x) = 2 x /5 - 1/5
d'où f ( - 2 ) = - 2 *2/5 - 1/5 = - 4/5 - 1/5 = - 5/5 = - 1