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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,*,*,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,24.1.3,弧、弦、圆心角,核心目标,.,2,1,课前预习,.,3,课堂导学,.,4,5,课后巩固,.,能力培优,.,24.1.3 弧、弦、圆心角核心目标.21,1,核心目标,了解弧、弦、圆心角之间的关系，并会利用这些关系进行简单的证明和计算,核心目标 了解弧、弦、圆心角之间的关系，并会利用,2,课前预习,1,顶点在,_,的角叫圆心角,2,在同圆或等圆中，相等的圆心角所对的,_,相等，所对的,_,也相等,3,在同圆或等圆中，如果两条弧相等，那么它们所对的,_,_,_,相等，所对的,_,相等,4,在同圆或等圆中，如果两条弦相等，那么它们所对的,_,_,_,相等，所对的,_,相等,弦,圆心,弧,弦,圆心角,圆心角,弧,课前预习1顶点在_的角叫圆心角弦圆心弧,3,课堂导学,【例题】如右图，以,ABCD,的顶点,A,为圆心，,AB,为半径作,A,，,A,交,AD,、,BC,于,E,、,F,，延长,BA,交,A,于,G.,求证：,GE,EF.,(,(,【解析】要证,GE,EF,，由弧、弦、圆心角的关系定理知只需证,GE,与,EF,所对的圆心角相等或弦,GE,EF.,(,(,(,(,课堂导学【例题】如右图，以ABCD的顶点A为圆心，AB为半,4,课堂导学,【答案】证明：连接,AF.,AB,AF,，,ABF,AFB,，,ABCD,中，,AD,BC,，,GAE,ABF,，,EAF,AFB,，,GAE,EAF,，,GE,EF,.,(,(,【点拔】在圆中求解圆心角、弧、弦等问题时，常运用它们三者之间的等对等关系进行转化，这是解题的常用方法,课堂导学【答案】证明：连接AF.(【点拔】在圆中求解圆心角、,5,课堂导学,对点训练,1,如下图，已知,BD,是,O,的直径，,点,A,、,C,在,O,上，,AB,BC,，,AOB,60,，则,BOC,_,度,(,(,2,如图，在,O,中，,AB,AC,，,A,40,，,则,B,_,度,(,(,60,70,课堂导学对点训练(2如图，在O中，ABAC，A40,6,课堂导学,3,如上图，,D,、,E,分别是,O,的半径,OA,、,OB,上的点，,CD,OA,，,CE,OB,，,CD,CE,，则,AC,与,CB,的大小关系是,(,),A,AC,CB,B,AC,CB,C,AC,CB,D,不能确定,(,(,(,(,(,(,(,(,B,课堂导学3如上图，D、E分别是O的半径OA、OB上的点，,7,课堂导学,4,如下图，已知,AB,、,CD,是,O,的直径，,E,是,O,上的一点，,BD,CE.,求证：,AC,CE,(,(,AOC,BOD,，,AC,BD,又,BD,CE,，,AC,CE,，,AC,CE,(,(,(,(,(,(,课堂导学4如下图，已知AB、CD是O的直径，E是O上的,8,课后巩固,5,如下图，已知在,O,中，,BC,是直径，,AB,DC,，,AOD,80,，则,ABC,等于,(,),A,40,B,65,C,100,D,105,(,(,6,如上图，已知,O,的半径等于,1,cm,，,AB,是直径，,C,，,D,是,O,上的两点，且,AD,DC,CB,则四边形,ABCD,的周长等于,(,),A,4cm B,5cm C,6cm D,7cm,(,(,(,B,B,课后巩固5如下图，已知在O中，BC(6如上图，已知O,9,课后巩固,7,如右下图，在,O,中，,AB,CD,，则下列结论错误的是,(,),A,AB,CD,B,AC,BD,C,AC,BD,D,AD,BD,(,(,(,(,D,课后巩固7如右下图，在O中，ABCD，则下列结论错误的,10,课后巩固,8,如下图，在,O,中，,CD,为,O,的直径，,AC,BC,，点,E,为,OD,上任意一点,(,不与,O,、,D,重合,),求证：,AE,BE.,(,(,AC,BC,，,AOC,BOC,AOD,BOD,，,又,OA,OB,，,OE,OE,，,得,AOE,BOE,，,AE,BE,(,(,课后巩固8如下图，在O中，CD为O的直径，ACBC，,11,课后巩固,9,如下图，已知,AB,是,O,的弦，半径,OC,、,OD,与,AB,分别交于点,E,、,F,，且,AE,BF.,求证：,AC,BD.,(,(,连接,OA,、,OB,，,由,OA,OB,得,A,B,又,AE,BF,，,AOE,BOF,，,AOE,BOF,，,AC,BD,(,(,课后巩固9如下图，已知AB是O的弦，半径OC、OD与AB,12,课后巩固,10,(2017,牡丹江,),如下图，在,O,中，,AC,CB,，,CD,OA,于,D,，,CE,OB,于,E,，求证：,AD,BE.,(,(,证明：连接,OC,，,AC,CB,，,AOC,BOC,CDOA,于,D,CE,OB,于,E,CDO,CEO,90,在,COD,与,COE,中，,COD,COE(AAS),，,OD,OE,，,AO,BO,，,AD,BE,(,(,DOC,EOC,CDO,CEO,90,CO,CO,课后巩固10(2017牡丹江)如下图，在O中，ACC,13,课后巩固,11,如下图，,AB,是圆,O,的直径，,D,是圆上的一点，,DOB,75,，,DC,交,BA,的延长线于,E,，交半圆于,C,，且,CE,AO,，求,E,的度数,解：连结,OC,，如图，,CE,AO,，,而,OA,OC,，,OC,EC,，,E,1,，,2,E,1,2E,，,OC,OD,，,D,2,2E,，,BOD,E,D,，,E,2E,75,，,E,25,课后巩固11如下图，AB是圆O的直径，D是圆上的一点，D,14,能力培优,(,(,(1),若,AC,BD,，求证：,AM,BN,；,12,如下图，在,O,中，,C,、,D,是直径,AB,上两点，,MCAB,，,ND,AB,，,M,，,N,在,O,上,连接,OM,、,ON,，,OA,OB,，,AC,BD,，,OC,OD,，,Rt,OCM,Rt,ODN,，,COM,DOM,，,AM,BN,(,(,能力培优(1)若ACBD，求证：AMBN；,15,能力培优,(,(2),若,C,，,D,分别为,OA,、,OB,的中点，试判断,AM,MN,NB,是否成立,?,说明你的理由,(,(,(,(,(,成立，理由：连接,AM,，,MC,OA,，,AC,OC,，,MC,垂直平分,OA,，,AM,OM,OA,，,AOM,是等边三角形，,AOM,60,，,同理,BON,60,，,MON,60,，,AOM,MON,BON,，,AM,MN,BN,能力培优(2)若C，D分别为OA、OB的中点，试判断AM,16,感谢聆听,感谢聆听,17,全文结束！再见,o study whether experiences during teen years would influence adult health.,So they followed 171 teens,starting when the kids were just 13.They interviewed each one every year for five years，and also spoke to these teens closest friends，who provided additional information about the quality of their friendships.The same 171 people were interviewed again at ages 25,26 and 27.This time,the questions surveyed each persons overall health.When the researchers analyzed the data,they found a strong connection between a teens behavior and adult health.Teens who had close friends grew up to be the healthier adults.Whether teens held back their feelings or expressed them to close friends also influenced later health.Those who held back their feelings were more likely to be sick as adults.The connection held up even after the scientists accounted for other possible influences on health.Weight，family income and drug use were all examined.So were mental health issues，such as anxiety and depression.And in these people，such other factors did not explain adult health as well as teen friendships did.,Getting along with the crowd may have benefits,says Allen,but there are also drawbacks.Teens who are more independent tend to do better at school and work.And peer pressure may lead some kids to engage in risky behavior,such as smoking,drinking or using drugs.Dealing with it is an ongoing challenge，Allen acknowledges.“Finding the right balance is the key.Teens shouldnt lose heart for not finding this easy.”And,he adds，“Parents need to be understanding about the pressures teens face.”,全文结束！再见o study whether experie,18,
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