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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
