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#1 2016-10-18 18:00:43

mathattack
Member
Registered: 2016-03-07
Posts: 17

Functions and Continuity

I'm having a little bit of difficulty with this question.  Could someone give some advice?

Consider the function:

f(x) = 1/b if x is rational and x = a/b in lowest terms and b>0
and f(x) = 0 if x is irrational.

Show that f(x) is continuous exactly at irrational points.



My thoughts so far: If a/b is in lowest terms, I'm guessing it means that and a and b are relatively prime?  So b would equal a/x, when x is a rational number?  I'm then getting that f(x) = x/a, when x is a rational number, but why would this not be continuous for any intervals?  Shouldn't the interval of a from (0,1] work at least? 

Any help would be much appreciated!

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#2 2016-10-18 19:43:11

thickhead
Member
Registered: 2016-04-16
Posts: 1,086

Re: Functions and Continuity

I was surprised to see continuity at irrational point because I had always thought irrational space isolated and discontinuous but on thinking it looks otherwise.e.g


{1}Vasudhaiva Kutumakam.{The whole Universe is a family.}
(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha
{Gods rejoice at those places where ladies are respected.}

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#3 2016-10-19 07:14:35

mathattack
Member
Registered: 2016-03-07
Posts: 17

Re: Functions and Continuity

Thanks Thickhead!

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