《平方差公式》第二课时课件北师大版七年级下.ppt

第一章 整式的乘除 1.5 平方差公式（第2课时 ） Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 知识回顾 1、平方差公式： (a+b)(ab)=a2b2 2、公式的结构特点： 左边是两个二项式的乘积，即两数和与 这两数差的积；右边是两数的平方差。 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 3、应用平方差公式的注意事项： 1）注意平方差公式的适用范围 2）字母a、b可以是数，也可以是整式 3）注意计算过程中的符号和括号 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 活动探究一 a b 图1-3 如图1-3，边长为a的大正方形中有一个边长为b 的小正方形. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 活动探究一 a b 图1-3 （1）请表示图1-3中阴影部分的面积 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 活动探究一 a b a b 图1-3图1-4 （2）小颖将阴影部分拼成了一个长方形， 如图1-4，这个长方形的长和宽分别是多 少？你能表示出它的面积吗？ Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 活动探究一 a b a b 图1-3图1-4 （3）比较（1）（2）的结果，你能验证 平方差公式吗？ Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 活动探究二 1、计算下列各组算式，并观察它们的共同 特点 79= 1113= 7981= 88= 1212= 8080= 2、从以上过程中，你发现了什么规律？ 3、请用字母表示这一规律，你能说明它的 正确性吗？ Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例3 用平方差公式进行计算： （1）10397 ； （2）118122 （100+3 ） （100-3 ） （120-2 ） （120+2 ） Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 练一练 计算： （1）704696 ； （2）9.9 10.1 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例4 计算： （1）a2(a+b)(ab)+a2b2 （2）(2x-5)(2x+5)-2x(2x-3) Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 练一练 计算： （1）(x+2y)(x2y)+(x+1)(x1) （2）x(x-1)- Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 自我检测 计算： 1） 20011999 -20002 2）(3mn+1)(3mn-1)-8m2n2 3） - （x+8） Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 课堂小结 本节课你有哪些收获？ 还有那些困惑？ Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 作业 1. 教材习题1.10 2. 拓展作业： 计算 (21+1)( 22+1)(24+1)(28+1)(216+1)(232+1)(264+1) Evaluation only