UPSC Exam  >  UPSC Notes  >  Mathematics Optional Notes for UPSC  >  Real Number System

Real Number System | Mathematics Optional Notes for UPSC PDF Download

Download, print and study this document offline
Please wait while the PDF view is loading
 Page 1


Edurev123 
Real Analysis 
1. Real Number System 
1.1 Show that every open subset of ?? is a countable union of disjoint open 
intervals. 
(2013 : 14 Marks) 
Solution: 
Let ?? =?? be an open and let ?? ??? . Then ?? is rational or irrational. If ?? is rational, define 
?? ?? = ? ?
?? ?? ??? ??? ?? is open 
?? (Union of all open intervals in ?? containing ?? )  
Note that ?? ?? is simply the largest open interval containing ?? as it is union of disjoint open 
intervals (see figure below). 
 
If ?? is irrational, as ?? is open, ??>0 such that (?? -?? ,?? +?? )??? . 
As every interval contains a rational ??? ?(?? -?? ,?? +?? ) and then ?? ??? ?? . 
???? ????? ??? ?? for some ?? ??? ??? , i.e., where ?? is a rational in ?? . 
?????????????????????????????????????????????????????????????????? ?UI
?? ??????? 
But                                                     ?? ?? =?? ??? 
?????????????????????????????????????????????????????????????????? = ?? ?? ?? ?? ??? ??? 
Page 2


Edurev123 
Real Analysis 
1. Real Number System 
1.1 Show that every open subset of ?? is a countable union of disjoint open 
intervals. 
(2013 : 14 Marks) 
Solution: 
Let ?? =?? be an open and let ?? ??? . Then ?? is rational or irrational. If ?? is rational, define 
?? ?? = ? ?
?? ?? ??? ??? ?? is open 
?? (Union of all open intervals in ?? containing ?? )  
Note that ?? ?? is simply the largest open interval containing ?? as it is union of disjoint open 
intervals (see figure below). 
 
If ?? is irrational, as ?? is open, ??>0 such that (?? -?? ,?? +?? )??? . 
As every interval contains a rational ??? ?(?? -?? ,?? +?? ) and then ?? ??? ?? . 
???? ????? ??? ?? for some ?? ??? ??? , i.e., where ?? is a rational in ?? . 
?????????????????????????????????????????????????????????????????? ?UI
?? ??????? 
But                                                     ?? ?? =?? ??? 
?????????????????????????????????????????????????????????????????? = ?? ?? ?? ?? ??? ??? 
And as the number of rationals in ?? are countable ?? can be writien as union of countable 
intervals. Also each of ?? ?? is disjoint as it being maximal if two ?? ?? overlap they will be 
same. 
  
Read More
387 videos|203 docs

Top Courses for UPSC

FAQs on Real Number System - Mathematics Optional Notes for UPSC

1. What are real numbers in the number system?
Ans. Real numbers are all the numbers on the number line, including both rational and irrational numbers. They can be represented as decimals or fractions.
2. How are real numbers classified in the number system?
Ans. Real numbers are classified into rational numbers and irrational numbers. Rational numbers can be expressed as fractions, while irrational numbers cannot be expressed as fractions.
3. Can real numbers be negative?
Ans. Yes, real numbers can be negative. They can be represented on the number line to the left of zero.
4. Are integers considered real numbers in the number system?
Ans. Yes, integers are considered real numbers. They are whole numbers that can be positive, negative, or zero.
5. How are real numbers used in practical applications?
Ans. Real numbers are used in various real-life applications such as measurements, calculations, and financial transactions. They are essential in fields like science, engineering, and economics.
387 videos|203 docs
Download as PDF
Explore Courses for UPSC exam

Top Courses for UPSC

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Sample Paper

,

Exam

,

Real Number System | Mathematics Optional Notes for UPSC

,

Previous Year Questions with Solutions

,

ppt

,

pdf

,

video lectures

,

mock tests for examination

,

Real Number System | Mathematics Optional Notes for UPSC

,

Extra Questions

,

Summary

,

Real Number System | Mathematics Optional Notes for UPSC

,

study material

,

practice quizzes

,

MCQs

,

Objective type Questions

,

shortcuts and tricks

,

past year papers

,

Viva Questions

,

Important questions

,

Semester Notes

,

Free

;