Rt△ABC中,∠A=90°,AD⊥BC于D,P为AD的中点,延长BP交AC于E,过E作EF⊥BC于F.求证:EF2=AE•EC.

问题描述:

Rt△ABC中,∠A=90°,AD⊥BC于D,P为AD的中点,延长BP交AC于E,过E作EF⊥BC于F.求证:EF2=AE•EC.

如图:延长FE交BA的延长线于H,

∵AD⊥BC,EF⊥BC,
∴AD∥HF

HE
AP
=
BE
BP
EF
DP
=
BE
BP

HE
AP
=
EF
DP

∵P为AD的中点,
∴AP=DP,
∴HE=EF
∵∠AEH=∠CEF,
∴Rt△AEH∽Rt△FEC,
AE
FE
=
HE
EC
,即
AE
EF
=
EF
EC

∴EF2=AE•EC.