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.
答
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
,即HE EC
=AE EF
,EF EC
∴EF2=AE•EC.