bonjour
1 ) 31 - 20 = 11
donc largeur = 11/2 = 5.5
longueur = x
largeur = ( 31 - 2 x ) / 2 = 15.5 - x
aire = x ( 15.5 - x ) = 15.5 x - x²
f (x) = x ( 15.5 - x ) = - x² + 15.5 x
f ( 4) = - ( 4)² + 15.5 * 4 = - 16 + 62 = 46
f ( 5) = - ( 5)² + 15.5 * 5 = - 25 + 77.5 = 52.5
le reste est de la lecture graphique,
