人教版八年级上册第十三章 轴对称13.2 画轴对称图形13.2.1 作轴对称图形教案

这是一份人教版八年级上册第十三章 轴对称13.2 画轴对称图形13.2.1 作轴对称图形教案，共5页。
轴对称图形              项目设计内容备 注课时第  1课时课 型新课教具三角板、刻度尺、圆规 教学目标知识与能力通过实际操作，掌握作轴对称图形的方法 过程与方法探索画一般的轴对称图形的方法，使学生能够作出简单平面图形经过一次对称后的图形 态度与情感培养审美情趣，培养合作意识和学习兴趣 重点画轴对称图形．   难点画轴对称图形．   教学手段方法动手操作，讲练结合 教学过程教师活动学生活动说明或设计意图情境导入  想一想   观察你画的图形：新图形和原图形有什么关系？对称轴是：折痕所在的直线，既直线l 图中的直线l与PP′有什么关系？            学生观察思考得出结论 新知教学 我们可由一个图形得到与它成轴对称的另一个图形，重复此过程，可得到美丽的图案.                  对称轴的方向和位置发生变化,得到图形的方向和位置也会发生变化.                如果有一 个图形和一条直线，如何作出与这个图形关于这条直线对称的图形呢？   已知对称轴 l 和一个点A，如何画出点A关于 l 的对称点A′ ?作法:  如图，过点A作对称轴 l的垂线，垂足为O;(2) 在垂线上截取 O A´= OA .点 A´就是点A关于直线 l的对应点.      例1：如图，已知△ABC和直线l ，作出与△ABC关于直线l对称的图形。分析：△ABC可以由三个顶点的位置确定，只要能分别作出这三个顶点关于直线l的对称点，连接这些对称点，就能得到要作的图形。      三、欣赏图片                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               学生完成作图  如何画线段AB关于直线l 的对称线段A′B′?作法：1、过点A作直线l的垂线，垂足为点O，在垂线上截OA′=OA，点A′就是点A关于直线l的对称点；   2、类似地，作出点B关于直线l的对称点B′；3、连接A′B′.                        学生欣赏图片，观察它们的造型                                               课堂练习 练习  已知四边形ABCD和直线l，作出与四边形ABCD关于直线l对称的图形．               学生独立完成，学生板演       通过练习对知识进一步掌握课堂小结作已知图形关于已知直线对称的图形的一般步聚:1、找点（确定图形中的一些特殊点）；2、画点（画出特殊点关于已知直线的对称点）3、连线（连接对称点） 由一个平面图形可以得到它关于一条直线l成轴对称的图形，这个图形与原图形的形状、大小完全相同；新图形上的每一点，都是原图形上的某一点关于直线L的对称点；连接任意一 对对应点的线段被对称轴垂直平分。 课外作业 1、用纸片剪一个三角形，分别沿它一边的中线、高、角平分线对折，看看哪些部分能够重合，哪些部分不能重合.2、教材习题13.2第一题  板书设计                    画轴对称图形1、情境引入2、探究新知3、课堂练习4、课堂小结5布置作业   课后反思