Set is a basic term in Mathematics. There is no precise definition for term “set”, But roughly speaking, a set is a collection of objects, Things or symbols, which are clearly defined. Set The objects are called the elements or members the set. Usually capital letters are used to denote sets and small letter are used to write elements.

We say “ the set of days in the week.” Yes, because it is clear whether elements are the days in the week. Sun d a y Mon da y Tues da y Wedne sda y Thurs da y Frid a y Satur da y

We say “ The set of letter in the English alphabet.” a b cd e... Yes, because it is clear whether elements are the letters in the English alphabet. x y z

The set of vowels in the English alphabet. a e i ou Yes, because it is clear whether elements are the vowels in the English alphabet.

State wheather each of the following collections is well-defined set. Give a reason for your answer. A book well-liked by my classmaters. No, because a book may be well-liked by some, but not other. A Mathematics teacher in my class. yes, because it is clear whether someone is a mathematics teacher in the class.

เซตของคนที่ หล่อที่สุด เป็นการใช้เซตที่ไม่ถูกต้อง เนื่องจาก คำว่า หล่อ ของแต่ละ บุคคลนั้น อาจไม่ตรงกันจึงทำให้ไม่สามารถ ระบุสมาชิกได้ เซตของคนที่ ฉลาดที่สุด เป็นการใช้เซตที่ไม่ถูกต้อง เนื่องจาก คำว่า ฉลาด ของแต่ละ บุคคลนั้น อาจไม่ตรงกัน จึงทำให้ไม่สามารถ ระบุสมาชิกที่แน่นอนได้

Example 2 List all the elements in each of the following sets. The set of positive integer more than 1 and less than 5 The elements of this set be 2 The set of positive even numbers less than 10 The elements of this set be 2 เซตของพยัญชนะในคำว่า “ พงษ์ศักดิ์ ” สมาชิกของ เซตนี้คือ พ, 3, 4, 4, 6, 8, ง, ด, ษ, ศ, ก

In Mathematics, a set, or appropriately the elements of a set, must be clearly defined, so that we can find our whether an object is a member of a set. There are two ways of doing this. 1. Listing the elements. (Tabular form, Roaster Method) The set can be defined by listing all its elements, Separated by commas and enclosed within braces. Representat ion of a set

Let A is the set of vowels in the English alphabet. Exam ple 3 A = {a, e, i, o, u} Let B is the set the month of the year there are 30 days. Exam ple 4 B = {April, June, September, November} Let C is the set of letter in the English alphabet. Exam ple 5 C = {a, b, c,..., z}

Let D is the set of positive even numbers. Exam ple 6 D = {2, 4, 6, 8, 10,...} Exam ple 7 Writing the following sets by listing the elements (Tabular form, Roaster Method) A is the set of integer numbers. A = {..., -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5,...} B is the set of positive integer numbers less than 1,000. B = {1, 2, 3, 4, 5,..., 999}

A = {a, e, i, o, u} a is a member of the set A. a  A (read a belongs to A) e is a member of the set A. e  A (read e belongs to A) b is not a member of the set A. b  A (read b does not belongs to A) p is not a member of the set A. p  A (read p does not belongs to A)

B = {2, 4, 6, 8, 10,...} 20 is a member of the set B. 20  B (read 20 belongs to B) 100 is a member of the set B. 100  B (read 100 belongs to B) 25 is not a member of the set B. 25  B (read 25 does not belongs to B) 99 is not a member of the set B. 99  B (read 99 does not belongs to B)

2. Describing the elements. (Set Builder form, Rule Method) The set can be defined, where possible, by describing the elements clearly. Set Builder form {x | builder of x} x belong to a setsuch that คิดให้ไกลไปให้ถึง ศึกษาการเขียนเซตต่อ …

Exam ple 8 A เป็นเซตพยัญชนะใน คำว่า “ นักเรียน ” A = {x | x เป็นพยัญชนะ ในคำว่า “ นักเรียน ”} B is the set of positive integer numbers less than 100. B = {x | x is positive integer numbers less than 100} B = {x | x เป็นจำนวนเต็มบวกที่ น้อยกว่า 100} C = {a, b, c,..., z} C = {x | x is a letter of the English alphabet}

A = {1, 2, 3, 4, 5, 6, 7, 8, 9} Exam ple 9 A = {x | x is natural numbers less than 10} A = {x | x เป็นจำนวน ธรรมชาติที่น้อยกว่า 10} A = {x | x เป็นจำนวนนับที่ น้อยกว่า 10} A = {x | x เป็นจำนวนเต็ม บวกที่น้อยกว่า 10} A = {x | x  I +, x < 10} B = {2, -2} B = {x | x  I, x 2 = 4} B = {x | x  I และ x 2 = 4}

C = {1, 4, 6, 8, 9, 10, 12, 14} C = {x |x is positive integer less than 15 and x is not prime} C = {x |x  I, x < 15, x  P} D = {February} D = {x |x is the month of the year with fewer than 30 days} “ เรียนรู้วิธีจับปลาดีกว่าการ รับปลามาจากผู้อื่น ”

M = {January, June, July} M = {x |x is the months whose names start with the letter J} E = {3, 6, 9,..., 54} E = {x  I + | x = 3n, n = 1, 2, 3,..., 18} E = {x  I | x = 3n, n  N, n  18}