bonjour,
f ( -2) = 5 et f ( 1) = 6
( 6 - 5 ) / ( 1 + 2 ) = 1/3
ax= x /3
f ( -2) = 5
- 2 /3 + b = 5
b = 15/3 + 2/3 = 17/3
f (x) = x /3 + 17 /3
d'où f ( 1) = 1/3 + 17/3 = 18/3 = 6
f ( -1 ) = - 1/3 + 17/3 = 16/3
f 5) = 5/3 + 17/3 = 22 /3
x/3 + 17/3 = 0
x /3 = - 17/3
3 x = - 51
x = - 51/3 = - 17
f ( - 17) = 0
x /3 + 17/3 = 6
x /3 = 18/3 - 17/3
x / 3 = 1/3
3 x = 3
x = 1