题目

—Did our school football team win the game as we had expected?—No, it was so . They lost the game by playing too riskily. 答案：【1】disappointing如图，AB是⊙O的直径，弦BD与CA延长线交于E点，EF⊥BA延长线于F，若∠AED=30°（I）求∠AFD的大小；（II）求证：AB2=BE•BD-AE•AC．