bonjour
i ( - 2 ) = 12 et i ( 7) = 15
( 15 - 12 ) / ( 7 + 2) = 3/9 = 1 /3
ax = x /3
- 2 * 1/3 + b = 12
b = 12 + 2/3 = 36/3 + 2/3 = 38/3
i (x) = x /3 + 38 /3
i ( 7) = 7 * 1/3 + 38/3 = 7/3 + 38/3 = 45/3 = 15
i ( - 5 ) = - 5 * 1/3 + 38/3 = - 5/3 + 38/3 = - 33 /3 = - 11
f ( -5 )= - 11