1.如图,AD是△ABC的高,AE是△ABC的外接圆直径.
求证:ABAC = AEAD
证明:连结BE
∵ AE⊙O的直径,ADBC
ABE = = 90
∵ E =
△ABE ∽ △
( )
ABAC = AEAD
2.如图,由直径AB的端点A引两弦AC、AD,延长AC、AD和过B点的切线分别交于E、F
求证:
证明:连结CB
∵ AB是直径,EF与圆相切于点B
ACB = ABE = 90
EAB + E = EAB + ABC = 90
ABC = )
又 ∵ ABC = )
( ) = ( )
∵ CAD = FAE
△ ( ) ∽ △ ( )
3.如图,已知D为△ABC的BC边上一点,且ADB = BAC,过D、C的圆交AC于E,连BE,与圆交于F点。
求证:AB 2 = BFBE
证明: ∵ ADB = BAC,ABD = ABC
△ ( ) ∽ △ ( )
∵ BDBC = BFBE
AB 2 = BFBE
4. 如图,已知AD是圆的弦,( ) ,DE是圆的切线且与弦AB的延长线相交于点E.
求证:AD 2 = ACAE
证明:连结BD
5. 如图,⊙O是△ABC的外接圆,BAC的平分线与BC边和外接圆分别相交于D和E.
求证:ADEC = ACBD
证明:
6. 如图,AB为⊙O的直径,CFAB于E,交⊙O于D,AF交⊙O于G.
求证:ACDG = AGDF
证明:连结CG
7. 如图,PD切⊙O于D,PC = PD,B为⊙O上一点,PB交⊙O于A,连结AC、BC.
求证:ACPB = PCBC
证明: