5.质数和合数.pptx

1、,R五年级下册,3.质数和合数 第 1 课时 质数和合数,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,考考你！,自然数 1-20 中，奇数有哪些？偶数有哪些？,奇数：1,3,5,7,9,11,13,15,17,19,偶数：2,4,6,8,10,12

2、,14,16,18,20,你知道它们是按什么标准分类的吗？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,试一试,请学号为 1-12 的同学说出你学号的因数是多少。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1 的因数：,2 的因数：,3 的因数：,4 的

3、因数：,5 的因数：,6 的因数：,7 的因数：,8 的因数：,9 的因数：,10 的因数：,11 的因数：,12 的因数：,1,1,2,1,3,1,2,4,1,5,1,2,3,6,1,7,1,2,4,8,1,3,9,1,2,5,10,1,11,1,2,3,4,6,12,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1,2,3,5,7,11,4,6,8,9,10,12,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路

4、,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,一个数，如果只有1和它本身两个因数，这样的数叫做质数（或素数）。如2，3，5，7都是质数。,一个数，如果除了1和它本身还有别的因数，这样的数叫做合数。如4，6，15，49都是合数。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1. 质数和合数的概念中“只有”和“除了还有

5、”是什么意思？,2. 1 是质数吗？是合数吗？为什么？,3. 要判断一个数是质数还是合数，关键要看什么？,1既不是质数也不是合数。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,1. 根据质数和合数的概念判断，27 是质数还是合数？说出理由。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成

6、才路,状元成才路,状元成才路,2. 判断下列各数是质数还是合数。 17 22 29 31 35 37 40 87 93 96,质数：17,29,31,37,合数：22,35,40,87,93,96,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,3. 说一说 1-20 的自然数中有哪些是质数。,1 3 5 7 9 11 13 15 17 19,0 2 4 6 8 10 12 14 16 18 20,熟记 20 以内的质数（2，3

7、，5，7，11，13，17，19）,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,观察上表，我们发现：,1 3 5 7 9 11 13 15 17 19,0 2 4 6 8 10 12 14 16 18 20,最小的偶数是（ ）,最小的奇数是（ ）,最小的质数是（ ）,最小的合数是（ ）,既是偶数又是质数的数只有（ ）,0,1,2,4,2,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元

8、成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,4. 思考下面的说法是否正确，说明理由。 （1）所有的奇数都是质数； （2）所有的质数都是奇数； （3）所有的合数都是偶数； （4）所有的偶数都是合数。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,找出100以内的质数，做一个质数表,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成

9、才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,划去2的倍数（2除外）,划去3的倍数（3除外）,划去5的倍数（5除外）,划去7的倍数（7除外）,划去1,100 以内质数表,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,100 以内质数表,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成

10、才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,100以内质数歌,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。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,知识运用,我会分类,在自然数 1-20 中 奇数： 偶数： 质数： 合数：,1,3,

11、5,7,9,11,13,15,17,19,2,4,6,8,10,12,14,16,18,20,2,3,5,7,11,13,17,19,4,6,8,9,10,12,14,15,16,18,20,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,你知道它们各是多少吗？,1. 两个质数，和是10，积是21，这两个质数是多少？,2. 两个质数，和是 7 ，积是10，这两个质数是多少？,3 和 7,2 和 5,状元成才路,状元成才路,状元成

12、才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,你知道它们各是多少吗？,3. 一个是最小质数，一个是最小合数。,4. 两个质数的和是30，这两个质数可能是几和几？,2 和 4,13 和 17 或 11 和 19,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,我会判断,在自然数中，除了质数以外都是合数。 两个质数的和一定是偶数。 一个合数至少有3个因数。 1既不是质数，也不是合数。 在自然数中，有无限多个质数，没有最大的质数。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,说一说,通过本节课的学习，你有哪些