人教版2020年春四年级下册数学第3单元《第1课时 加法运算定律》

第1课时加法运算定律运算定律3优翼wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com在加法算式302050中3020和50分别叫什么30和20叫做加数50叫做它们的和复习导入一wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com根据所给的条件你能提出什么数学问题吗1探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com李叔叔今天一共骑了多少千米40565640564096405696上午和下午的路程和是多少得数是一样的下午和上午的路程和是多少探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com请同学们开动脑筋再想一些类似的算式探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100c

omwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com观察每组算式等号两边有什么相同点和不同点数没变符号没有变只是加数位置发生了变化问题1像这样的算式你写的完么探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com请大家用自己喜欢的方式表示加法交换律问题2这些算式有什么共同的特点这就叫做加法交换律两个数相加交换加数的位置和不变探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com通常我们数学上可以用字母表示数今天我们就选字母a和b来表示两个加数a表示第一个加数b表示第二个加数用字母就可以表示成abba比如探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com这里有三组算式在○里填上适当的符号121314○121314302860○302860320150230○320150230观察这三个等式它们有什么相同的地方探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com等号左右两边的算式在运算

顺序上有什么不同但它们的结果怎样从以上问题你发现了什么规律121314○121314302860○302860320150230○320150230大家发现的这个规律我们把它叫做加法结合律探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com三个数相加先把前两个数相加或者先把后两个数相加和不变这叫做加法结合律abcabc字母abc分别表示三个加数那么加法结合律表示为探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com这三天一共骑了多少路程88104＋962探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com怎样计算比较简便要应用什么运算定律 方法 快递客服问题件处理详细方法山木方法pdf计算方法pdf华与华方法下载八字理论方法下载 188＋104＋9619296288探索新知二wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com方法288＋104＋96＝88＋104＋96＝88200288→应用加法结合律上边两种方法在应用运算定律方面有什么不同第一道是按从左到右的顺序计算而第二道应用了加法结合律探索新知二wwwyouyi100comwwwyouyi100comwwwyo

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两个数相加交换加数的位置和不变这叫做加法交换律用字母可以表示为abba三个数相加先把前两个数相加或者先把后两个数相加和不变这叫做加法结合律用字母表示为abcabc课堂小结四wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com课后练习五wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com课后练习五wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com3678135296＋7813529636问题观察一下表中的数有什么特点3先计算再填表72114171332374431592213270431156213374114171332课后练习五wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com4新风商场第一季度电器销售情况统计表13378481118课后练习五wwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100comwwwyouyi100com课后练习五