2-5的倍数的特征

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,*,你能找出下面哪些数是,2,的倍数，哪些数是,5,的倍数吗？,15,、,25,、,18,、,30,、,20,、,49,、,36,2,的倍数有：,5,的倍数有：,15,25,30,20,18,30,20,36,这有什么了不起的？我不用计算就能判断出一个多位数是不是,2,或,5,的倍数！,32584796,、,523869425,523869425,是,5,的倍数。,32584796,是,2,的倍数。,3258,.,47962=1629,.,2398,5,.,2386,.,94255=1,.,0477,.,3885,2,，,5,的倍数的特征,探索活动（一）,执教人：肖和平,我们可以先写出几个,5,的倍数来看看。,对，先研究小范围的数，再进行推广验证。,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,1,、从,1100,的数表中找出,5,的倍数，做上记号。,2,、观察你找到的,5,的倍数,猜测,5,的倍数的特征是什么？,研究步骤：,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,个位上是,0,或,5,的数是,5,的倍数。,猜测：,在所有的自然数中，,5,的倍数都是个位是,0,或,5,的数吗？,如何验证？,找几个个位是,0,或,5,的大数，除以,5,看看。如果商是整数而没有余数，就证明是,5,的倍数。同时证明了,5,的倍数的特征对于大数也成立。,490,675,3250,43275,5=98,5=135,5=650,5=8655,490,、,675,、,3250,、,43275,都是,5,的倍数。,个位上是,0,或,5,的数都是,5,的倍数。,经过验证，我们得出了什么结论？,在下面的数中找出,5,的倍数。,45 53 80 75 34,89 95 65 71,回想一下：我们刚才是怎么研究,5,的倍数的特征的？,先确定一个小范围进行研究。（找出,1100,中所有,5,的倍数，发现其特征。）,验证较大的数也具有此特征。（举例）,得出结论。（个位上是,0,或,5,的数都是,5,的倍数。）,2,的倍数有什么特征？,你能像刚才那样进行研究吗？,1.,在,1100,的数表中找出,2,的倍数，做上记号。,2.,观察、猜测,2,的倍数的特征。,3.,举例验证你的发现对更大的数成立吗？,4.,举例验证，得出结论。,研究步骤：,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,2,12,22,32,42,52,62,72,82,92,4,14,24,34,44,54,64,74,84,94,6,16,26,36,46,56,66,76,86,96,8,18,28,38,48,58,68,78,88,98,10,20,30,40,50,60,70,80,90,100,个位上是,0,、,2,、,4,、,6,、,8,的数，都是,2,的倍数。,2,的倍数的特征,:,猜测,520,682,举例验证,2=260,2=341,838,2=419,946,2=473,1034,2=517,个位上是,0,、,2,、,4,、,6,、,8,的数，都是,2,的倍数。,得出结论,2,的倍数的特征：,是,2,的倍数的数叫偶数。,不是,2,的倍数的数叫奇数。,你知道吗？,0,也是偶数。,自 然 数,偶 数,奇 数,这些数是奇数还是偶数？,39,（,偶数,）,46,23,54,18,75,33,96,（奇数）,（奇数）,（奇数）,（奇数）,（,偶数,）,（,偶数,）,（,偶数,）,只要个位上是,0,、,2,、,4,、,6,、,8,的数，就是偶数。,偶数都是双数，奇数都是单数，,在,28,、,35,、,40,、,55,、,10,、,84,、,95,、,78,、,53,、,90,中，,2,的倍数有：,5,的倍数有：,28,、,40,、,10,、,84,、,78,、,90,35,、,40,、,55,、,10,、,95,、,90,既是,2,的倍数又是,5,的倍数的有：,40,、,10,、,90,既是,2,的倍数又是,5,的倍数的数的个位是,0.,它们都是,10,的倍数。,既是,2,的倍数又是,5,的倍数的有：,40,、,10,、,90,任选两个数字组成符合下面要求的数。,4 0 7 5,奇数：,偶数：,2,的倍数：,5,的倍数：,既是,2,的倍数，又是,5,的倍数：,47,、,45,、,75,、,57,、,74,、,54,、,70,、,50,、,74,、,54,、,70,、,50,、,45,、,75,、,70,、,50,、,40,、,40,、,40,、,70,、,50,、,40,、,收获：,我们研究了什么？,2,的倍数特征。,5,的倍数特征。,什么是偶数，,什么是奇数。,先研究小范围的数，,最后得出结论。,再举例验证，,是怎样研究的？,再 见,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,