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找最小公倍数,北师版,五年级数学上册,情境导入,你还记得怎样找一个数的倍数吗？,7 1=7,7 2=14,.,探究新知,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,在下表中用“”标出,4,的倍数，用“”标出,6,的倍数。,4,的倍数有,6,的倍数有,哪些数既标有“”又标有“”？这些数有什么特点？,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,我们把两个数的“共同倍数”称作这两个数的“,公倍数,”。其中最小的一个是它们的“,最小公倍数,”。,认一认，填一填。,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,4,和,6,的公倍数有,_,。,4,和,6,的最小公倍数是,_,。,12,24,36,48,12,淘气用下面的方法表示公倍数，你能看懂吗？,集合法,4,8,16,12,24,20,6,12,18,24,30,4,的倍数,6,的倍数,4,8,16,12,24,20,6,18,30,4,和,6,的公倍数,12,24,列举法,4,的倍数,:4,8,12,16,20,24,28,32,36,40,44,48,6,的倍数,:6,12,18,24,30,36,42,48,其中,4,和,6,最小公倍数是,12,。,筛选法,6,的倍数：,6,12,18,24,30,36,42,48,.,其中,4,和,6,最小公倍数是,12,。,随堂练习,1.,在下表中用“”标出,3,的倍数，用“”标出,5,的倍数。,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,哪些数上既标有“”又标有“”？这些数有什么特点？,【,选自教材,P82,练一练第,1,题,】,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,3,和,5,的公倍数有,15,30,45,，它们的最小公倍数是,15,。,2.,1,2,3,4,5,6,7,8,9,10,8,8,16,6,6,12,24,32,40,48,56,64,72,80,18,24,30,36,42,48,54,60,50,以内,6,和,8,的公倍数有,，最小公倍数是,。,24,，,48,24,【,选自教材,P82,练一练第,2,题,】,3.,想一想，填一填。,6,和,9,的最小公倍数是多少？,6,12,18,24,30,36,42,48,9,18,27,36,，,45,18,36,50,以内,6,的倍数,50,以内,9,的倍数,50,以内,6,和,9,的公倍数,6,12,24,30,42,48,9,27,45,【,选自教材,P82,练一练第,3,题,】,4.,求下面各组数的最小公倍数。,3,和,6,8,和,10,2,和,7,6,和,10,3,的倍数：,3,6,9,12,.,6,的倍数：,6,12,18,.,3,和,6,的公倍数：,6,12,.,3,和,6,的最小公倍数就是,6,。,两个数互为倍数关系，那么大的那个数就是这组数的最小公倍数。,【,选自教材,P82,练一练第,4,题,】,4.,求下面各组数的最小公倍数。,3,和,6,8,和,10,2,和,7,6,和,10,8,的倍数：,8,16,24,32,40,.,10,的倍数：,10,20,30,40,.,8,和,10,的最小公倍数就是,40,。,4.,求下面各组数的最小公倍数。,3,和,6,8,和,10,2,和,7,6,和,10,2,的倍数：,2,4,6,8,10,12,14,.,7,的倍数：,7,14,21,28,.,2,和,7,的最小公倍数就是,14,。,两个数都是质数的时候，它们的最小公倍数就是两个数的乘积。,4.,求下面各组数的最小公倍数。,3,和,6,8,和,10,2,和,7,6,和,10,6,的倍数：,6,12,18,24,30,.,10,的倍数：,10,20,30,.,6,和,10,的最小公倍数就是,30,。,课堂小结,知识点：,我们把两个数的“共同倍数”称作这两个数的“,公倍数,”。,其中最小的一个是它们的“,最小公倍数,”。,集合法表示最小公倍数：,
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