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1、,質(zhì)數(shù)和合數(shù),蘇教版五年級數(shù)學下冊,寫出下面各數(shù)的所有因數(shù)。,在這些數(shù)中,因數(shù)只有兩個的有(,2,,,3,,,5,);,2,的因數(shù),:,5,的因數(shù),:,8,的因數(shù),:,3,的因數(shù),:,6,的因數(shù),:,9,的因數(shù),:,1,2,1,3,1,5,1,2,3,6,1,2,4,8,1,3,9,只有兩個因數(shù)的數(shù),它們的因數(shù)有什么特點?,1,它本身 素數(shù)(或質(zhì)數(shù)),因數(shù)超過兩個的有(,6,,,8,,,9,)。,例,6,8,的因數(shù),:,6,的因數(shù),:,9,的因數(shù),:,2,的因數(shù),:,5,的因數(shù),:,3,的因數(shù),:,1,2,1,3,1,5,1,2,3,6,1,2,4,8,1,3,9,這些數(shù)的因數(shù)與素數(shù)的因數(shù)有什
2、么不同?,除了,1,和它本身還有別的因數(shù) 合數(shù),1,它本身 (或素數(shù)),這樣的數(shù)叫,這樣的數(shù)叫質(zhì)數(shù),只有,和,兩個因數(shù),。,。,例,6,寫出下面各數(shù)的所有因數(shù)。,“,1,”,的因數(shù)有幾個?,“,1,”,是質(zhì)數(shù)嗎?,“,1,”,是合數(shù)嗎?,1,的因數(shù)只有,1,個。,1,既不是質(zhì)數(shù),也不是合數(shù)。,想一想:,(,3,)你能用集合圖表示所有的非零自然數(shù)嗎?,(,1,)素數(shù)的因數(shù)有幾個?合數(shù)的因數(shù)呢?,(,2,)如果自然數(shù)不斷地增加,可能歸到哪一類?有沒有可能出現(xiàn)第四類情況?,(,1,)質(zhì)數(shù)的因數(shù)有,2,個,合數(shù)的因數(shù)有,3,個或,3,個以上。,(,2,)如果自然數(shù)不斷地增加,可能是素數(shù)也可能是合數(shù);不
3、可能出現(xiàn)第四類情況。,素數(shù) 合數(shù),1,(,3,)用集合圖表示:,先找出,4,、,7,和,10,的所有因數(shù),再寫出這三個數(shù)分別是素數(shù)還是合數(shù)。,4,的因數(shù)有:,,4,是()數(shù)。,7,的因數(shù)有:,,7,是()數(shù)。,10,的因數(shù)有:,,10,是()數(shù)。,1,2,4,合,1,7,素,1,2,5,10,合,試一試,10,以內(nèi)的質(zhì)數(shù)有:,2,,,3,,,5,,,7,。,先找出,1120,各數(shù)的所有因數(shù),再把,1120,分別填入圈里。,11,的因數(shù)有,13,的因數(shù)有,15,的因數(shù)有,17,的因數(shù)有,19,的因數(shù)有,12,的因數(shù)有,14,的因數(shù)有,16,的因數(shù)有,18,的因數(shù)有,20,的因數(shù)有,素數(shù),合數(shù),1
4、,11,1,13,1,3,5,15,1,17,1,19,1,2,3,4,6,12,1,2,7,14,1,2,4,8,16,1,2,3,6,9,18,1,2,4,5,10,20,12,14,15,16,18,20,11,13,17,19,想想做做,從,2,至,50,的數(shù)中,先劃掉,2,的倍數(shù),再依次劃掉,3,、,5,、,7,的倍數(shù)(但,2,、,3,、,5,、,7,本身不劃掉)。,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,4
5、1,42,43,44,45,46,47,48,49,50,想想做做,下面各數(shù),哪些是質(zhì)數(shù),哪些是合數(shù)。,21 23 25 27 29 31,33 35 37 39 47 49,想想做做,質(zhì) 數(shù) 表,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,先找出,4,、,7,和,10,的所有因數(shù),再寫出這三個數(shù)分別是質(zhì)數(shù)還是合數(shù)。,4,的因數(shù)有:,,4,是()數(shù)。,7,的因數(shù)有
6、:,,7,是()數(shù)。,10,的因數(shù)有:,,10,是()數(shù)。,試一試,先找出,1120,各數(shù)的所有因數(shù),再把,1120,分別填入圈里。,11,的因數(shù)有,13,的因數(shù)有,15,的因數(shù)有,17,的因數(shù)有,19,的因數(shù)有,12,的因數(shù)有,14,的因數(shù)有,16,的因數(shù)有,18,的因數(shù)有,20,的因數(shù)有,質(zhì)數(shù),合數(shù),想想做做,(,1,)每位同學每次要認真聽清老師說什么。,(,2,)認真觀察每次活動,從活動中你能發(fā)現(xiàn)什么?,游戲要求:,(,1,)請學號是偶數(shù)的同學起立,其中是質(zhì)數(shù)的到講臺左邊,合數(shù)的到講臺右邊。,游戲活動:,(2,)請學號是奇數(shù)的同學起立,其 中是質(zhì)數(shù)的到講臺左邊,合數(shù)的到講臺右邊。,偶數(shù)除了,2,之外,都是合數(shù)。,奇數(shù)里既有質(zhì)數(shù),也有合數(shù)。,1是奇數(shù),但它既不是質(zhì)數(shù)也不是合數(shù)。,合數(shù)不一定是偶數(shù),但質(zhì)數(shù)除,2,以外都是奇數(shù)。,1,2,39,53,100,奇數(shù),偶數(shù),質(zhì)數(shù),合數(shù),判斷:對的打“”,錯的打“,”,。,