素数合数与分解素因数.pptx

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,#,1.2,素数、合数与分解素因数,我们来观察下列每个数的因数个数,：,1,，,2,，,3,，,4,，,5,，,6,，,7,，,8,，,9,，,10,，,11,，,12,，,13,，,14,，,15,，,16,，,17,，,18,，,19,，,20,有,一个因数,的：,1,有,两个因数,的：,2,、,3,、,5,、,7,有,两个以上因数,的：,4,、,6,、,9,、,8,、,10,1,，既不是素数,也不是合数,除了,1,和它本身,还有其他因数,的数叫做,合数,只有,1,和它本身,两个因数,的数叫做素（,质）数素数,合数,正整数,（,按因数的个数分类,）,1,素数,合数,1,、判断下面各数,哪些是素数,?,哪些是合数,?,17 22 29 35 37 87,2,、,为什么？,素数：,17 29 37,*,只有,1,和它本身两个因数,*,除了,1,和它本身还有别的因数,合数：,22 35 87,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,5556,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,100,以内有哪些素数？,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,先去掉,1,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,5455,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,划去,2,的倍数,（,2,除外）,2,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,95,97,99,9,15,21,27,33,39,45,51,57,63,69,75,81,87,93,99,划去,3,的倍数,（,3,除外）,2,3,5,7,11,13,17,19,23,25,29,31,35,37,41,43,47,49,53,55,59,61,65,67,71,73,77,79,83,85,89,91,95,97,25,35,55,65,85,95,划去,5,的倍数,（,5,除外）,2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,49,53,59,61,67,71,73,77,79,83,89,91,97,49,77,91,划去,7,的倍数,（,7除外）,2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,100,以内有哪些素数？,3 5 7,11 13 17 19,29 31 37 41 43 47,53 59 61 67 71 73 79,83 89 97,100,以内的质数表,2 3,5 6,你能把,30,写成几个素数相乘的形式吗？,30,56,，,6,23,30,15,2,3,5,30,30,235,每个合数都可以写,成几个,(),数相乘的,形式,其中每个素数都是,这个合数的,(),数,叫,做这个合数的,素因数,。,素,因,13X4=5213,和,4,都是,52,的因数吗？,13,和,4,都是,52,的,素因数,吗？,把一个合数用素因数,相乘的形式表示出来，,叫做,分解素因数,。,什么是分解素因数呢,?,自主练习,5,、用短除法把下面各数分解素因数。,18 25 28 34 1334,18,9,2,3,3,34,17,2,18,233,34,217,自主练习,6,、火眼金睛辨对错。,（,1,）一个非零的自然数，不是奇数就是偶数。,（）,（,2,）一个非零的自然数，不是素数就是合数。,（）,（,3,）大于,2,的偶数都是合数。（）,（,4,）所有的素数都是奇数。（）,X,X,思考：,（,1,）试求,225,的积的因数个数是多少？,（,2,）求,180,的因数个数,