bonjour,
1 ) f ( -3) = - 12 donc f (x ) = 12/3 = 4 f(x) = 4 x
2 ) 4 x = - 8
x = - 8/4 = - 2
3 ) g ( 1 ) = 12 et g ( 4) = 3
( 3 - 12 ) / ( 4 - 1 ) = - 9/3 = - 3 donc ax = - 3 x
g ( 1) = 12
1 * - 3 + b = 12
b = 12 + 3 = 15
g (x) = - 3 x + 15
d'où g ( 4) = - 3 *4 + 15 = - 12 + 15 = 3
g (5) = - 3*5 + 15 = - 15 + 15 = 0