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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,苏教版小学数学五年级下,质数和合数,3.1,是质数吗?是合数吗?,预习展示,1.,什么是质数?,2.,什么是合数?,通过预习,,,同学们知道非零自然数除,了分为,奇数、偶数外,,,还有别的分类方法吗?,大家知道什么样的数是质数,?,什么样的数是合数?,2,、,3,、,5,这几个数只有,1,和它本身两个数,像这样的数叫作,质数(或素数),。,6,、,8,、,9,这几个数除了,1,和它本身还有别的因数,像这样的数叫作,合数,。,想一想:,1,的因数有几个?,1,是质数吗?是合数吗?,1,的因数只有,1,个,。,1,既不是质数也不是合数。,1,,,2,1,,,3,1,,,5,1,,,2,,,3,,,6,1,,,2,,,4,,,8,1,,,3,,,9,2,,,3,,,5,6,,,8,,,9,自然数,质数,合数,只有两个因数,(,1,和它本身),。,1,因数超过两个,(除了,1,和它本身以外还有别的因数),。,只有一个因数,(只有,1,),。,(按,因数的个数,分类),质 数,合 数,(按,是不是,2的,倍数,分类),奇数,偶数,自然数,自然数,1,,,2,,,4,合,1,,,7,质,1,,,2,,,5,,,10,合,11,,,13,,,17,,,19,12,,,14,,,15,,,16,,,18,,,20,23,,,29,,,31,,,37,,,43,,,47,21,,,25,,,29,,,33,,,35,,,49,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,找出,100,以内的质数,,二三五七和十一,十三后面是十七,还有十九别忘记,二三九,三一七,四一,四三,四十七,五三九,六一七,七一,七三,七十九,八三,八九,九十七。,100,以内质数口诀,这节课你有什么收获?,课堂作业:,P39.3,课后作业:,预习第,38,页例,7,,例,8,。,
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