九年級數(shù)學(xué)上冊第二十四章圓241圓的有關(guān)性質(zhì)2413弧弦圓心角導(dǎo)學(xué)課件新版新人教版

1、24.1.3 弧、弦、圓心角核心目標(biāo).21課前預(yù)習(xí) .3課堂導(dǎo)學(xué) .45課后鞏固.能力培優(yōu).24.1.3 弧、弦、圓心角核心目標(biāo).21核心目標(biāo) 了解弧、弦、圓心角之間的關(guān)系，并會利用這些關(guān)系進(jìn)行簡單的證明和計算核心目標(biāo) 了解弧、弦、圓心角之間的關(guān)系，并會利用課前預(yù)習(xí)1頂點在_的角叫圓心角2在同圓或等圓中，相等的圓心角所對的_相等，所對的_也相等3在同圓或等圓中，如果兩條弧相等，那么它們所對的_相等，所對的_相等4在同圓或等圓中，如果兩條弦相等，那么它們所對的_相等，所對的_相等弦圓心弧弦圓心角圓心角弧課前預(yù)習(xí)1頂點在_的角叫圓心角弦圓心弧課堂導(dǎo)學(xué)【例題】如右圖，以ABCD的頂點A為圓心，AB為

2、半徑作A，A交AD、BC于E、F，延長BA交A于G. 求證：GEEF .(【解析】要證GEEF ，由弧、弦、圓心角的關(guān)系定理知只需證GE與EF所對的圓心角相等或弦GEEF.(課堂導(dǎo)學(xué)【例題】如右圖，以ABCD的頂點A為圓心，AB為半課堂導(dǎo)學(xué)【答案】證明：連接AF. ABAF，ABFAFB， ABCD中，ADBC， GAEABF，EAFAFB， GAEEAF， GEEF.(【點拔】在圓中求解圓心角、弧、弦等問題時，常運(yùn)用它們?nèi)咧g的等對等關(guān)系進(jìn)行轉(zhuǎn)化，這是解題的常用方法課堂導(dǎo)學(xué)【答案】證明：連接AF.(【點拔】在圓中求解圓心角、課堂導(dǎo)學(xué)對點訓(xùn)練1如下圖，已知BD是O的直徑， 點A、C在O上，A

3、BBC， AOB60，則BOC_度(2如圖，在O中，ABAC，A40， 則B_度(6070課堂導(dǎo)學(xué)對點訓(xùn)練(2如圖，在O中，ABAC，A40課堂導(dǎo)學(xué)3如上圖，D、E分別是O的半徑OA、OB上的點，CDOA，CEOB，CDCE，則AC與CB的大小關(guān)系是() AACCB BACCB CACCB D不能確定(B課堂導(dǎo)學(xué)3如上圖，D、E分別是O的半徑OA、OB上的點，課堂導(dǎo)學(xué)4如下圖，已知AB、CD是O的直徑，E是O上的一點，BDCE.求證：ACCE(AOCBOD，ACBD又BDCE，ACCE，ACCE(課堂導(dǎo)學(xué)4如下圖，已知AB、CD是O的直徑，E是O上的課后鞏固5如下圖，已知在O中，BC 是直徑，

4、ABDC，AOD 80，則ABC等于() A40 B65 C100 D105(6如上圖，已知O的半徑等于 1cm，AB是直徑，C，D是 O上的兩點，且ADDCCB, 則四邊形ABCD的周長等于() A4cm B5cm C6cm D7cm(BB課后鞏固5如下圖，已知在O中，BC(6如上圖，已知O課后鞏固7如右下圖，在O中，ABCD，則下列結(jié)論錯誤的是() AABCD BACBD CACBD DADBD(D課后鞏固7如右下圖，在O中，ABCD，則下列結(jié)論錯誤的課后鞏固8如下圖，在O中，CD為O的直徑，ACBC，點E為OD上任意一點(不與O、D重合) 求證：AEBE.(ACBC，AOCBOCAODB

5、OD，又OAOB，OEOE，得AOEBOE，AEBE(課后鞏固8如下圖，在O中，CD為O的直徑，ACBC，課后鞏固9如下圖，已知AB是O的弦，半徑OC、OD與AB分別交于點E、F，且AEBF. 求證：ACBD.(連接OA、OB，由OAOB得AB又AEBF，AOEBOF，AOEBOF，ACBD(課后鞏固9如下圖，已知AB是O的弦，半徑OC、OD與AB課后鞏固10(2017牡丹江)如下圖，在O中，ACCB，CDOA于D，CEOB于E，求證：ADBE.(證明：連接OC，ACCB，AOCBOCCDOA于D,CEOB于E,CDOCEO90在COD與COE中， , CODCOE(AAS)，ODOE，AOB

6、O，ADBE(DOCEOCCDOCEO90COCO課后鞏固10(2017牡丹江)如下圖，在O中，ACC課后鞏固11如下圖，AB是圓O的直徑，D是圓上的一點，DOB75，DC交BA的延長線于E，交半圓于C，且CEAO，求E的度數(shù)解：連結(jié)OC，如圖，CEAO，而OAOC，OCEC，E1，2E12E，OCOD，D22E，BODED，E2E75，E25課后鞏固11如下圖，AB是圓O的直徑，D是圓上的一點，D能力培優(yōu)( (1)若ACBD，求證：AMBN ； 12如下圖，在O中，C、D是直徑AB上兩點，MCAB，NDAB，M，N在O上連接OM、ON，OAOB，ACBD，OCOD，RtOCMRtODN，CO

7、MDOM，AMBN(能力培優(yōu)( (1)若ACBD，求證：AMBN ；能力培優(yōu)(2)若C，D分別為OA、OB的中點，試判斷AMMN NB是否成立?說明你的理由(成立，理由：連接AM，MCOA，ACOC，MC垂直平分OA，AMOMOA，AOM是等邊三角形，AOM60，同理BON60，MON60，AOMMONBON， AMMNBN能力培優(yōu)(2)若C，D分別為OA、OB的中點，試判斷AM感謝聆聽感謝聆聽全文結(jié)束！再見o study whether experiences during teen years would influence adult health.So they followed 17

8、1 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

9、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

10、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

11、 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