已知:如图,P是⊙O直径AB延长线上一点,过P的直线交⊙O于C、D两点,弦DF⊥AB于点H,CF交AB于点E。 ⑴
已知:如图,P是⊙O直径AB延长线上一点,过P的直线交⊙O于C、D两点,弦DF⊥AB于点H,CF交AB于点E。⑴求证:PC·PD=PO·PE;⑵若DE⊥CF,∠P=150...
已知:如图,P是⊙O直径AB延长线上一点,过P的直线交⊙O于C、D两点,弦DF⊥AB于点H,CF交AB于点E。 ⑴ 求证:PC·PD=PO·PE;⑵ 若DE⊥CF,∠P=15 0 ,⊙O的半径为2,求弦CF的长
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2014-09-08
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(1)证明略 (2) |
(1) 证明:连结DO, ∵直径AB⊥DF, ∴ AD=AF ∴∠DOA=∠DCF ∵∠DOP+∠DOA=180 O , ∠PCE+∠DCF=180 O ∴ ∠DOP=∠ECP……(2分) ∵∠P=∠P ∴ΔPOD∽ΔPCE ∴ ![](https://iknow-pic.cdn.bcebos.com/42a98226cffc1e170bd1c4834990f603738de912?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) 即PC·PD=PO·PE……(2分) (2)解:∵直径AB⊥DF,∴ DH="FH " ∴ ED=EF ∴ EH平分∠DEF ∵ DE⊥CF ∴ ∠DEC=∠DEF=90 O ∴ ∠FEH=45 O ∠CEP=45 O ∵ ∠DCE=∠P+∠CEP=15 O +45 O =60 O ∴ ∠DOH=60 O ……(2分) 在RtΔDOH中,由sin60 O = ∴ DH= ![](https://iknow-pic.cdn.bcebos.com/b8014a90f603738d2f244490b01bb051f819ec12?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ∴ DH= ∵ ![](https://iknow-pic.cdn.bcebos.com/728da9773912b31b3902859b8518367adab4e112?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ∴ ∴ ![](https://iknow-pic.cdn.bcebos.com/4a36acaf2edda3cc84e8f09202e93901213f9270?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ……(2分) 在RtΔDCF中,由 ∴ ∴ ![](https://iknow-pic.cdn.bcebos.com/3801213fb80e7becabd64b532c2eb9389b506b70?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto) ……(1分) |
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