Question

如图ab是圆o的直径df切圆o于dbf⊥df过点a做ac平行bf交BD的延长线于c

Answer 1

连接OD,∵DF是切线,∴OD⊥DF,∵BF⊥DF,∴BF∥OD,∴∠DBF=∠BDO,∵OB=OD,∴∠BDO=∠OBD,∴∠OBD=∠DBF,∵AC∥BF,∴∠C=∠DBF=∠OBD,∴AC=AB.⑵∠C=∠OBD=∠GBD=30°,连接AD、BE,∵AB是直径,∴∠E=∠ADB=90°,∴AD=1/2...