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1、平面几何1.(崇文·理·题3)已知是的切线,切点为,,是的直径,交于点,,则的半径为()A. B. C. D.【解析】C;于是圆的半径为.2.(东城·理·题3)如图,已知是⊙的一条弦,点为上一点,,交⊙于,若,,则的长是()A.B.C.D.【解析】B;延长交于圆上一点,得到一条圆的弦,易知点为该弦的中点,有.3.(丰台·理·题9)在平行四边形中,点是边的中点,与交于点,若的面积是,则的面积是.【解析】4;取的中点,连结交于,则∵且,∴四边形为平行四边形∴∴4.(海淀·理·题10)otherstaffoftheCentre.Duringthew
2、ar,ZhuwastransferredbacktoJiangxi,andDirectorofthenewOfficeinJingdezhen,JiangxiCommitteeSecretary.Startingin1939servedasrecorderoftheWestNorthOrganization,SecretaryoftheSpecialCommitteeAfterthevictoryofthelongMarch,hehasbeentheNorthwestOfficeoftheFederationofStateenterprisesMinister,Shen
3、mufuguSARmissions,DirectorofNingxiaCountypartyCommitteeSecretaryandrecorderoftheCountypartyCommitteeSecretary,Ministersand21如图,为的直径,且,为的中点,过作的弦,且,则弦的长度为.【解析】7;由得.由已知和相交弦定理得,解得.于是.1.(石景山·理·题10)已知曲线的参数方程为,则曲线的普通方程是;点在曲线上,点在平面区域上,则的最小值是.【解析】,;是圆;不等式组的可行域如图阴影所示,点为、为时,最短,长度是.2.(西城·理·题12)如图,切于
4、点,割线经过圆心,弦于点.已知的半径为3,,则..otherstaffoftheCentre.Duringthewar,ZhuwastransferredbacktoJiangxi,andDirectorofthenewOfficeinJingdezhen,JiangxiCommitteeSecretary.Startingin1939servedasrecorderoftheWestNorthOrganization,SecretaryoftheSpecialCommitteeAfterthevictoryofthelongMarch,hehasbeentheNort
5、hwestOfficeoftheFederationofStateenterprisesMinister,ShenmufuguSARmissions,DirectorofNingxiaCountypartyCommitteeSecretaryandrecorderoftheCountypartyCommitteeSecretary,Ministersand21【解析】;;连结,知,于是,.1.(宣武·理·题11)若是上三点,切于点,,则的大小为.【解析】;如图,弦切角,于是,从而.2.(朝阳·理·题12)如图,圆是的外接圆,过点的切线交的延长线于点,,则的长为;的长为.
6、【解析】..又由知.于是.即.3.(西城·理·题12)如图,切于点,割线经过圆心,弦于点.已知的半径为3,,则..otherstaffoftheCentre.Duringthewar,ZhuwastransferredbacktoJiangxi,andDirectorofthenewOfficeinJingdezhen,JiangxiCommitteeSecretary.Startingin1939servedasrecorderoftheWestNorthOrganization,SecretaryoftheSpecialCommitteeAfterthevictor
7、yofthelongMarch,hehasbeentheNorthwestOfficeoftheFederationofStateenterprisesMinister,ShenmufuguSARmissions,DirectorofNingxiaCountypartyCommitteeSecretaryandrecorderoftheCountypartyCommitteeSecretary,Ministersand21【解析】;;连结,知,于是,.坐标系与参数方程1.(海淀·理·题4)在平面直角坐标系中,点的直角坐标为.若以原点为极点