题目内容
如图,AB是⊙O的直径,点C、D在⊙O上,∠BOC=110°,AD∥OC,则∠AOD等于 ( )
A.70° B.60° C.50° D.40°
.D
已知如图,AB是半圆直经,△ACD内接于半⊙O,CE⊥AB于E,延长AD交EC的延长线于F,求证:AC·CD=AD·FC.