1. utilise le théorème de Thalès (PM)//(AB) car perpendiculaires à (AB)
PM/AC = PB/BA
PM/3 = x/4
PM = 3x/4 = (3/4)x
2. le périmètre APMQ
P=2(AP+PQ) = (4-x+0,75x) = 8-0,5x
3.a. P point de [AB]
AB = 4 ==> 0≤x≤4
b. 8-0,5x = 7 ==> x = 2 ok
8-0,5x = 4 ==> x = 8≥4 ca ne convient pas
8-0,5x = 10 ===> x =-2 ≤0 ca ne convient pas
