中考数学复习-第5单元-三角形-第21课时-等腰三角形与直角三角形教案1.doc

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1、ideological and theoretical qualities and practical working ability, and strive to build a contingent of league cadres with positive work style and high quality. Hold a regular meeting of the party secretary every fortnightly, arrange the work of the regiment, feedback the student information. Focus

2、 on training junior high school, junior high school secretary of the regiment branch to enable them to raise A firm political conviction, diligent and diligent learning spirit and practical and innovative work style.第五单元 三角形第21课时 等腰三角形及直角三角形教学目标【考试目标】1.了解等腰三角形的有关概念，掌握等腰三角形的性质和一个.三角形为等腰三角形的条件；了解等边三角形

3、的概念及性质；2.了解直角三角形的概念，掌握直角三角形的性质和一个三角形是直角三角形的条件；3.会运用勾股定理解决简单问题；会用勾股定理的逆定理判定一个三角形是否为直角三角形.【教学重点】1. 了解掌握等腰三角形的有关概念及性质.2. 学会等腰三角形的判定.3. 掌握等边三角形的性质及判定方法.4. 掌握线段垂直平分线与角平分线的相关性质.5. 学会直角三角形的相关性质与判定方法.教学过程一、 体系图引入，引发思考二、 引入真题、归纳考点【例1】（2016年菏泽）如图，ABC与ABC都是等腰三角形，且AB=AC=5，AB=AC=3，若B+B=90，则ABC与ABC的面积比为 （ A ）A25：

4、9 B5：3 C D.【解析】解：过A 作ADBC于D，过A作ADBC于D， ABC与ABC都是等腰三角形， B=C，B=C，BC=2BD，BC=2BD， AD=ABsinB，AD=ABsinB，BC=2BD=2ABcosB，BC=2BD=2ABcosB， B+B=90， sinB=cosB，sinB=cosB，SBAC=0.5ADBC=0.5ABsinB2ABcosB=25sinBcosB，SABC=0.5ADBC=ABcosB2ABsinB=9sinBcosB， SBAC：SABC=25：9故选A.【例2】（2016年苏州）如图，在ABC中，AB=10，B=60，点D、E分别在AB、BC上

5、，且BD=BE=4，将BDE沿DE所在直线折叠得到BDE（点B在四边形ADEC内），连接AB，则AB的长为_ .【解析】过点B作BFAD，垂足为F，因为BD=BE=4，B=60,所以BDE是等边三角形.由折叠的性质可得DB=BD=4，BDE=BDE=60，所以ADB=60，所以在RtBFD中，DF=2，BF= .因为AB=10，所以AF=4，所以【例3】（2016年西宁）如图，OP平分AOB，AOP=15，PCOA，OAPD于点D，PC=4 ，则,PD= 2 . 【解析】过点P作PEOB于点E.OP平分AOB，PD=PE，AOB=2AOP=30.PCOA，ECP=AOB=30，PE=0.5PC

6、=2，PD=PE=2.【例4】（2016年江西）如图是一张长方形纸片ABCD，已知AB=8，AD=7，E为AB上一点，AE=5，现要剪下一张等腰三角形纸片（AEP），使点P落在长方形ABCD的某一条边上，则等腰三角形AEP的底边长是 .【解析】据题意，如果点P落在AD边上，则AE=AP=5，底边长PE2=AP2+AE2=52+52=50，PE= ；如果点P落在DC边上，则底边长AE=5；如果点P落在BC边上，则两条腰AE=EP=5，所以所以等腰三角形AEP的底边长是 或5或 .三、师生互动，总结知识先小组内交流收获和感想，而后以小组为单位派代表进行总结.教师作以补充.课后作业布置作业：同步导练

7、教学反思学生对特殊三角形的掌握情况很好，望多加复习巩固，做到熟练会用.Strengthen the team connection, strengthen the knowledge education among the students (especially the first grade students), and promote the formation of good school spirit with the influence of the league members. All League branches should start with recommending

8、 outstanding students as the development objects of the League, take amateur league schools as the basis, conscientiously do a good job in the work of pre-league education, league membership education, League members vanguard exemplary consciousness education, excellent league members education, etc

9、. Under the premise of ensuring the quality, the development quantity of league members will increase steadily, and the ranks of league members in middle schools will be strengthened constantly. It is planned to develop a group of new league members in April and mid-October.2. Carry out the regular

10、meeting system of the League branch, and strengthen the ideological accomplishment and the training work in the field of business. League cadres are the backbone of the work of the League, and their quality directly affects the quality of the work. Therefore, they plan to use their extracurricular activities on Wednesday to open special training and other forms of study activities. To help the regiment cadres improve their ideological quality and professional skills, improve their3