Bonjour,
Situation 1 :
Pythagore : AD² = AC²-CD² = 9 donc AD = 3
donc AE = AD/2 = 3/2
Pythagore : AB² = AE² - BE² = (3/2)²-1² = 9/4 - 1 = 5/4 = 1,25
donc AB = √1,25
Situation 2 :
Thalès : AB/AC = BE/CD
donc : AB = AC × BE/CD = 5 × 1/4 = 1,25
