prime numbers and sum numbers.docVIP

Prime Numbers and Sum Numbers 质数和合数 　 Teaching Contents: Book 10 of PES人教版小学数学第十册Teaching Aims: Help the students to understand the essence of prime numbers and sum numbers. Learn the way to judge a number a prime number or a sum number. 教学目标:使学生理解质数,合数的意义, 掌握判断一个数是质数还是合数的方法。 Teaching Procedures: 教学步骤 I. Revision 复习 “Look at these numbers. Do they have any divisors besides 1 and itself? If they do, please tell me one.” “下列各数, 除了1与它本身这两个约数, 还有没有别的约数? 如果有, 说出一个就行” “Except 1 and itself, 8 has a divisor: 2” “8 除了1 和它本身以外, 还有约数2” 或直接说 “2” “Except 1 and itself, 19 has no divisors.” “19 除了1 和它本身以外, 没有别的约数” 或直接答 “没有” II. Presentation 新授 1. T: If I want to classify the natural numbers from 1 to 12, what shall I do? 师: 如果我想把1-12 的自然数分类, 可以怎样分? Ss: Whether divisible by two or not, we may divide natural numbers into odd numbers and even numbers. 生: 根据能否被2 整除将自然数分为奇数、偶数 板书: Natural Numbers odd numbers even numbers writing: 自然数奇数偶数 Today we are going to classify natural numbers by seeing how many divisors they have. 今天, 我们学习根据一个数约数的个数来对自然数进行分类 板书: Natural Numbers classify by how many divisors they have writing: 自然数 根据约数的个数分类 2. Classification 分类 Can we classify these numbers according to their divisors? Please write down the divisors of the numbers from 1 to 12. Then decide how many groups you can classify. “能否根据约数的个数来将这些数分类?” Two is a divisor of 2,4,6,8,10 and 12, but it isn’t a divisor of 1,3,5,7,9 and 11.So we may classify them??? into two types. “分两类, 2、4、6、8、10、12都有约数2 为一类, 1、3、5、7、9、11都没有约数2为另一类。” Because some numbers have two divisors, but some have more than two, we may classify them into two types. “分两类。有的只有两个约数，有的不止两个约数。” Who agrees with him? Please come to the front to classify the numbers. “谁与他的想法一样？上黑板来分分类” 学生上黑板将卡片归类。 3. 归纳提示课题 (1) Look at these numbers. What is the law of their divisors? 这些数, (师手指2、3、5、7、11) 的约数有什么规律? They have two divisors: 1 and themselves. “只有1 和它本身两个约数” 指名说。 Wha