bonjour
f ( 2) = 1 et f ( - 3 ) = 4
( 4 - 1 ) / ( - 3 - 2 ) = - 3/ 5
ax = - 3 x /5
f ( 2) = 1
2 * - 3 /5 + b = 1
- 6 /5 + b = 1
b = 1 + 6 /5 = 11/5 = 2.2
f (x) = - 3 x /5 + 2.2
d'où f ( - 3 ) = - 3 * - 3/5 + 2 .2 = 9/5 + 2.2 = 4
fonction décroissante
f ( - 1/2 ) = - 1/2 * - 3 /5 + 2.2 = 3/10 + 2.2 = 2.5
- 3 x /5 + 2.2 ≥ - 2
- 3 x / 5 ≥ - 2 - 2 .2
- 3 x /5 ≥ - 4.4
- 3 x / 5 ≥ 22 / 5
- 3 x ≥ 22
x ≤ - 22/3