[三角形复习shangke.ppt

* 欢迎各位评委同仁莅临指导 东台市许河镇中学 王国兵 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. 1.请同学在纸上各画一个三个内角分别为40°，60 °，80 °的锐角三角形，画好后，同桌之间比比看，你会发现什么？ 2.下面再请同学们在纸上画两边长分别为4cm和6cm，且长度为4cm的边所对应的角为30 °的三角形，你发现了什么？ 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. 沿着右边图中的虚线，分别把右面的图形划分为两个全等图形，并与同伴进行交流。 (至少找出两种方法) 活动 探索 ? 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. 做一做: 我们看看下面的几种划分方法，与你的划分 方法对比一下，看看自己是如何划分的。 图形一划分方法 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. 一、挖掘“隐含条件”判全等 1.如图（1），AB=CD，AC=BD，则与∠ACB相等的角是 ,为什么？ 2.如图（2），点D在AB上，点E在AC上，CD与BE相交于点O，且AD=AE,AB=AC.若∠B=20°,CD=5cm，则∠C= ,BE= . 3.如图（3），若OB=OD，∠A=∠C，若AB=3cm，则CD= . A D B C 图（1） B C O D E A 图（2） A D B C O 图（3） ∠DBC 20° 5cm 3cm 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. 二、熟练转化“间接条件”判全等 4.如图（4）AE=CF，∠AFD=∠CEB，DF=BE，△AFD与△ CEB全等吗？为什么？ 5.如图（5）∠CAE=∠BAD，∠B=∠D，AC=AE，△ABC与△ADE全等吗？为什么？ 6.“三月三，放风筝”如图（6）是小东同学自己做的风筝，他根据AB=AD,BC=DC，不用度量，就知道∠ABC=∠ADC。请用所学的知识给予说明。 A D B C F E A C E B D 解答 Evaluation only. Created with A