Verified answer

1) AC/AE = AB/AD ⇔ AC x AD = AE x AB ⇒ AD = AE x AB/AC = 4.5 x 4/3 = 6 cm

AD = 6 cm

2) AC/AE = BC/DE ⇔ AC x DE = AE x BC ⇒ BC = AC x DE/AE = 3 x 4.2/4.5 = 2.8 cm

BC = 2.8 cm

3) on applique la réciproque du théorème de Thalès

AC/AF = AB/AG

3/4.05 = 4/5.4

  0.74 = 0.74 ⇒ (BC) // (FG)