中考数学压轴题详解—圆(6)

复习圆

（3）证明：连结OC交BD于G由（2）得四边形OBCD是菱形， ∴OC BD且OG GC． ···························································································· 8分 又已知OB＝BH ， ∴BG∥CH． ········································································ 9分 ∴ OCH OGB 90 ， ∴CH是⊙O的切线． ················································· 10分

5 解： （1）添加 AB=BD ····································································································· 2分

∴∠BDE =∠BCD ·∵AB=BD ∴ ············································································ 3分 AB=BD又∵∠DBE =∠DBC ∴△BDE∽△BCD

BDBE

································································································································ 4分 BCBD

的中点 ·（2）若AB∥DO，点D所在的位置是BC···························································· 5分

∵AB∥DO ∴∠ADO =∠BAD ·················································································· 6分

=DC ·∵∠ADO =∠OAD ∴∠OAD =∠BAD ∴DB······················································· 7分

（3）在（1）和（2）的条件下，．

=DC ∴∠∵ BDA =∠DAC ∴ BD∥OA AB=BD

又∵AB∥DO ∴四边形AODB是平行四边形 ················································· 9分 ∵OA=OD ∴平行四边形AODB是菱形 ······················································ 10分

6 解：（1）FB＝FE ，PE＝PA ···································&