bonjour
a) largeur = ( 31 - 20) /2 = 5.5 cm
b ) longueur = x , BC = ( 31 - 2 x ) / 2 = 15.5 - x
c) aire = 10 x
f(x) = x ( 15.5 - x )
f (4) = 4 ( 15.5 - 4) = 4 * 11.5 = 46
x ( 15.5 - x ) = 0
15.5 x - x² = 0
- x² = - 15.5
x = √ 15.5 ou - √15.5
pour la suite, il suffit de lire le graphique
