bonjour

f ( 9) = 2

f ( -1) = environ 1.2

f ( x) = 1

f ( 6) = 1          pourquoi  0.6 ?

f ( - 3 ) = - 2

f ( - 3 ) = - 2  et  f (  9 ) = 2

( 2 + 2 ) / ( 9 + 3 ) = 4/12 = 1/3

ax =  x /3

f ( - 3) = - 2

- 3 *  1/3 + b = - 2

-  1  + b = - 2

b = - 2 + 1 = - 1

donc f (x) =   x /3 - 1

d'où  f ( 9) = 9  * 1/3 - 1 =  3 - 1 = 2

f ( - 1 ) =  - 1 * 1/3 - 1 = - 1 /3 - 3/3 = - 4/3