bonsoir
f ( 4) = 5 et f ( 2 ) = 3
( 3 - 5 ) / ( 2 - 4) = - 2 / - 2 = 1
2 * 1 + b = 3
2 + b = 3
b = 3 - 2 = 1
f (x) = x + 1
g (3) = 4 et g ( 0) = 5
( 5 - 4 ) / ( 0 - 3) = 1/-3 = - 1/3
3 *-1/3 + b = 4
- 3/3 + b = 4
b = 4 + 1 = 5
g (x) = - 1/3 x + 5
f (x) = g ( x)
x + 1 = - x /3 + 5
3 x / 3 + 3/3 = - x /3 + 15 /3
3 x + x = 15 - 3
4 x = 12
x = 3
les 2 fonctions sont égales pour x = 3