聂江华 2019-01-25 17:36
<p></p><h1><strong><span style="font-family: 宋体;font-size: 20px"><span style="font-family:宋体">乘法运算定律</span>---<span style="font-family:宋体">简便运算</span></span></strong></h1><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教学目标</span></span></p><p><span style="font-family:宋体;font-size:20px">1. </span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">使学生理解乘法的交换律、结合律和分配律各自的特点，通过体验、感悟，熟练、灵活地运用他们进行简便计算</span></span></p><p><span style="font-family:宋体;font-size:20px">2. </span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">感受数学与现实生活的联系，能用乘法运算定律解决在生活中简单的实际问题。</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教学重难点；</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">灵活应用乘法运算定律进行简单计算。</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教学过程</span></span></p><p><span style="font-family:宋体;font-size:20px">一、</span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">复习导入</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">我们先来复习一下学习过的乘法的运算定律，交换律、结合律、分配律，同学们一定比较熟悉吧！</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教师板书：</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">乘法交换律：</span>axb=bxa</span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">乘法结合律；</span>(axb)xc=ax(bxc)</span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">乘法分配律：</span>(a+b)xc=axc+bxc</span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">请同学们一定要牢记这些定律，一会儿要给大家带来很大的帮助。</span></span></p><p style="margin-left: 0;text-indent: 0"><span style="font-family:宋体;font-size:20px">二、</span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教授新课</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教学例一</span></span></p><p><span style="font-family:宋体;font-size:20px">(1) </span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">出示新课，让同学们自己观察图上问题，列出算式，请同学们用自己喜欢的方式算出结果，然后展示学生计算方法。</span></span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">学生一、</span>61x25x4 <span style="font-family:宋体">学生二、</span><span style="font-family:Calibri">61x25x4</span></span></p><p><span style=";font-family:宋体;font-size:20px"> =1525x4 =61x(25x4)</span></p><p><span style=";font-family:宋体;font-size:20px"> =6100 =61x100</span></p><p><span style=";font-family:宋体;font-size:20px"> =6100</span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">同学们讨论计算方法，谁的计算方法更快更准确。</span></span></p><p style="margin-left: 0;text-indent: 0"><span style="font-family:宋体;font-size:20px">(2) </span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">试一试</span></span></p><p style="text-indent: 60px"><span style=";font-family:宋体;font-size:20px">2x23x35 51x15x4 50x(19x8)</span></p><p><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">教学例二</span></span></p><p><span style="font-family:宋体;font-size:20px">（1）</span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">出示教材情境图，激发学生的学习兴趣。同学们观察，列出算式，看这个算式符合哪个运算定律形式</span>,102x45</span></p><p style="text-indent: 20px"><span style=";font-family:宋体;font-size:20px">(2) <span style="font-family:宋体">同学们动手，互相讨论</span></span></p><p style="text-indent: 37px"><span style=";font-family:宋体;font-size:20px">102x45</span></p><p><span style=";font-family:宋体;font-size:20px"> =(100+2)x45</span></p><p><span style=";font-family:宋体;font-size:19px"> =100x45+2x45</span></p><p><span style=";font-family:宋体;font-size:19px"> =4500+90</span></p><p><span style=";font-family:宋体;font-size:19px"> =4590</span></p><p><span style=";font-family:宋体;font-size:19px"><span style="font-family:宋体">教师；看到这个算式，你想到了应用什么定律？</span></span></p><p style="text-indent: 37px"><span style=";font-family:宋体;font-size:19px">32x27+32x73</span></p><p style="text-indent: 37px"><span style=";font-family:宋体;font-size:19px"><span style="font-family:宋体">仔细看一看这道题里的两个乘法计算中的因数有什么特点？想一想这道题怎样做才能使计算简便呢？</span></span></p><p style="text-indent: 37px"><span style=";font-family:宋体;font-size:19px"><span style="font-family:宋体">（两个乘法算式计算有相同因数</span>32<span style="font-family:宋体">，另外两个因数</span><span style="font-family:Calibri">27</span><span style="font-family:宋体">和</span><span style="font-family:Calibri">73</span><span style="font-family:宋体">，他们的和正好是</span><span style="font-family:Calibri">100</span><span style="font-family:宋体">，整百数乘以</span><span style="font-family:Calibri">32</span><span style="font-family:宋体">容易。应用乘法分配律比较简便）</span></span></p><p style="margin-left: 0;text-indent: 0"><span style="font-family:宋体;font-size:20px">三、</span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">课堂练习</span></span></p><p style="margin-left: 0;text-indent: 0"><span style="font-family:宋体;font-size:20px">四、</span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">课堂小结</span></span></p><p style="margin-left: 0;text-indent: 0"><span style="font-family:宋体;font-size:20px">五、</span><span style=";font-family:宋体;font-size:20px"><span style="font-family:宋体">布置作业</span></span></p><p><span style=";font-family:宋体;font-size:20px"> </span></p><p><br/></p>