3.
如图,AB是⊙O直径,C为⊙O上一点,AD垂直过C点的切线于点D,连接BC,过C点作CF⊥AB于点F.
(1)求证:CD=CF;
(2)若∠B=60°,CD=2$\sqrt{3}$,求⊙O的半径OB.
(1)求证:CD=CF;
(2)若∠B=60°,CD=2$\sqrt{3}$,求⊙O的半径OB.
16.
如图,AB为⊙O的直径,CA为⊙O的切线,CB交⊙O于D,$\widehat{AD}$=$\widehat{DE}$,AE交BD于F,若DF=BF,则tan∠BDE的值为( )
0 282787 282795 282801 282805 282811 282813 282817 282823 282825 282831 282837 282841 282843 282847 282853 282855 282861 282865 282867 282871 282873 282877 282879 282881 282882 282883 282885 282886 282887 282889 282891 282895 282897 282901 282903 282907 282913 282915 282921 282925 282927 282931 282937 282943 282945 282951 282955 282957 282963 282967 282973 282981 366461
| A. | $\frac{\sqrt{2}}{2}$ | B. | $\frac{\sqrt{2}}{4}$ | C. | $\frac{\sqrt{6}}{3}$ | D. | $\frac{\sqrt{3}}{3}$ |