解：連接?$EF，$??$AF，$??$AE$?
∵四邊形?$ABCD$?為?$⊙O$?的內(nèi)接四邊形
∴?$∠ABC+∠ADC=180°$?
∵?$BE，$??$DF $?分別平分?$∠ABC，$??$∠ADC$?
∴?$∠ABE=∠EBC，$??$∠ADF=∠CDF$?
∴?$2∠ABE+2∠ADF=180°$?
∴?$∠ABE+∠ADF=90°$?
∵?$∠ABE=∠AFE，$??$∠ADF=∠AEF$?
∴?$∠AFE+∠AEF=90°$?
∴?$∠F AE=90°$?
∴?$EF $?為?$⊙O$?的直徑
∴?$EF {過圓}O$?的圓心
