4.2线段长短的比较课件[北师大版版七年级上].ppt

Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 我比你高! 你哪有我高啊! 服了吧! 喔，原来你比我高! Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 考考你的眼力 A B C D 线段AB和线段CD哪一条长? Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 点D在AB的延长线上 点D与B重合 点D在AB上 ABCD AB=CD ABCD Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 例题1：如图,已知线段a, 用圆规和直尺画出线段AB , 使得AB=a 解: 1 、画射线AC; 2 、在射线AC上截取AB=a 线段AB就是所要画的线段。 以点A为圆心，a为半径画弧，交射线AC于点B Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 二、新课 1、（1）根据图填空 A· B C D （2）点B具有什么特殊位置?你能给它命名吗?并说出这一位置的特征. BC CD BC CD AB CD AC Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 如图 点M把线段AB分成相等的两条线段AM与BM，点M叫做线段AB的 。(midpoint) AM MB 1/2AB = = 中点 M· 反过来若M是AB的中点则有 AM= MB =1/2AB Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. （1） 小明到小英家有三条路可走，如图，你认为走那条路最近？ （2） （3） 答：走第(2)条路最短。 理由：两点之间的所有连线中，线段最短。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 在一条直线上顺次取A、B、C三点，使AB=5cm， BC=2cm,并且取线段AC的中点O，求线段OB的长。 A B C O 解： AC=AB+BC=5+2=7cm OB=AB-AO=5-3.5=1.5cm （或OB=OC-BC=3.5-2=1.5cm） 答：线段OB的长等于1.5cm. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 1、两点之间的所有连线中 最短。 2、两 点 之 间 线 段 的 长 度， 叫做 。（distance) 线段 这两点之间的距离 可得到以下结论 ： 线段的公理 Evaluation only. Created with Aspose.Slide