证明:
∵△ADE是等边三角形
∴AD=DE=AE,∠ADE=∠AED=60°
∴∠ADB=∠AEC=120°
∵∠BAC=120°=∠ADB,∠A=∠A
∴△ABD∽△CBA(AA)
∴AB/BC=BD/AB,∠BAD=∠C
∴AB²=BC×BD
∵∠BAD=∠C,∠ADB=∠AEC
∴△ABD∽△CAE(AA)
∴AD/CE =BD/AE
∴AD×AE=CE×BD
∵AD=AE=DE
∴DE²=CE×BD
∴DE²/AB²=(CE×BD)/(BC×BD)=CE/BC
证明:
∵△ADE是等边三角形
∴AD=DE=AE,∠ADE=∠AED=60°
∴∠ADB=∠AEC=120°
∵∠BAC=120°=∠ADB,∠A=∠A
∴△ABD∽△CBA(AA)
∴AB/BC=BD/AB,∠BAD=∠C
∴AB²=BC×BD
∵∠BAD=∠C,∠ADB=∠AEC
∴△ABD∽△CAE(AA)
∴AD/CE =BD/AE
∴AD×AE=CE×BD
∵AD=AE=DE
∴DE²=CE×BD
∴DE²/AB²=(CE×BD)/(BC×BD)=CE/BC