∵∠BAD=∠CAE,∠ADB=∠AEC=90
∴ΔADB∽ΔAEC
∴AD/AE=AB/AC
∴ΔADE∽ΔABC
∴∠AEP=∠ACF,DE/BC=AE/AC ①
又∴∠PAE=∠FAC
∴ΔPAE∽ΔFAC
∴AE/AC=AP/AF ②
由①②得DE:BC=AP:AF
∵∠BAD=∠CAE,∠ADB=∠AEC=90
∴ΔADB∽ΔAEC
∴AD/AE=AB/AC
∴ΔADE∽ΔABC
∴∠AEP=∠ACF,DE/BC=AE/AC ①
又∴∠PAE=∠FAC
∴ΔPAE∽ΔFAC
∴AE/AC=AP/AF ②
由①②得DE:BC=AP:AF