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乘法运算定律运算定律人教版四年级数学下册
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com(a×b)×c=a×(b×c)乘法结合律:三个数相乘,先乘前两个数或者先乘后两个数,积不变。乘法交换律:两个因数交换位置,积不变。a×b=b×a复习导入一
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com一共有多少名同学参加了这次植树活动?7探索新知二
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www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com从上面的算式中,你发现了什么规律?两个数的和与一个数相乘,可以先把他们分别与这个数相乘,再相加,结果不变。这叫做乘法分配律。探索新知二
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www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com1.下面哪些算式是正确的?正确的画“√”,错误的画“×”。56×(19+28)=56×19+28()32×(7×3)=32×7+32×3()64×64+36×64=(64+36)×64()××√巩固练习三
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com运用了乘法分配律。25×12=25×2+25×10502512×2503002.观察下面的竖式,说说在计算的过程中运用了什么运算定律。巩固练习三
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www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com两个数的和与一个数相乘,可以先把它们这个数分别相乘,再相加,这叫做乘法分配律,用字母表示为(a+b)×c=a×c+b×c。课堂小结四
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