1、The Concept of Set,08数本5班 Tence,When in the junior school ,we had gotten in touch with the set, such as the set of integers ,the set of rational numbers and the set of the values of the inequality x-73.But what is the concept of set? Is it just like the concept of ”together”?,Example 1. All the prim
2、e numbers between one and twenty. If we consider every prime number from one to twenty as element, all these elements are a set.,Example 2. Let each man-made satellite which was fired from 1991 to 2003 in China be an element, then all these elements make up a set, too.,Example 3. we suppose that eac
3、h right triangle is an element, so we can easily have a conclusion that all right triangles form a set.,DEFINITION OF A SET:In general, the object of discussion is called element, and the collection of some elements is called set.,Sets usually are denoted by capital letters: A, B, C,X, Y, Z; element
4、s are designated by lower-case letters: a, b, c,x, y, z. We use the special notationx S to mean that “x is an element of S” or “x belongs to S”. If x does not belong to S, we write that x S.,When convenient, we shall designate sets by displaying the elements in braces; for example, the set of positi
5、ve odd numbers less than 10 is denoted by the symbol 1,3,5,7,9.The method of listing the members of a set within braces is called roster notation.,But sometimes the elements of a set cant be list all, such as the set of the values of the inequality x-73. At the moment ,we can use another methoddescr
6、ibing.,Emphasize: Set is not collection.,Two important points: 1、That objects can make up a set is dependent on the two standards: being entirety and being certain.2、The elements of a set have three properties: certain, distinct and disorder.,Exercises:1、 if A=x x2=x, then -1_A.2、 if C=x N 1x10 , th
7、en 8_C, 9.1_C.3 、Please choose proper method to denote theseset:(1) the set of all prime numbers less than 8.(2) the set of the values of the inequality 4x-53.,Exercises:1、 if A=x x2=x, then -1_A.2、 if C=x N 1x10 , then 8_C, 9.1_C.3 、Please choose proper method to denote theseset:(1) the set of all
8、prime numbers less than 8.(2) the set of the values of the inequality 4x-53.,Conclusion : Today we have studied the concept of set and its expressing methods, properties. All these are basic concepts. Only we master these contents can we go deep into the study of set. So everybody shall do more exercise to consolidate the knowledge.,Home work : P6、3 Prepare next lesson,THE END! THANK YOU!,
