general question about intervals

[Sarahisme]

what is the difference between an open interval (i.e. (a,b) ) and a closed interval (i.e. [a,b] )??

 

does the open interval not contain the endpoints (i.e. a & b) or something like that? :S

 

Cheers

 

Sarah

[Crash]

The square brakets mean to but not including and the rounded brackets mean up to and including

[Sarahisme]

so open intervals contain enpoints, whereas closed intervals do not contain endpoints?

[Tom Mattson]

No, it's the other way around. Crash is wrong.

[Sarahisme]

so (a,b) is not including endpoints but [a,b] does?

[Tom Mattson]

That would indeed be "the other way around" from what Crash said.

 

Sarah, I have seen you post calculus questions on this board. You really ought to look up this basic information for yourself.

[Sarahisme]

i thought the whole point of this board was to get help when you don't understand something....even if it is something that other people may find 'basic'

[Tom Mattson]

What's not to understand? It's a definition. You understood it when you read it here, so you certainly would have understood it if you had looked it up. Furthermore, if you really don't understand what open and closed intervals are then you shouldn't be taking calculus, because that is most definitely prerequisite knowledge. But I think you are perfectly capable of understanding it. You just didn't feel like cracking open the book.

 

And the whole point of your education is to become self-sufficient. To learn how to think and to learn how to learn. Surely looking up a simple definition is not too taxing, eh?

 

And for the record: ordinarily I don't believe in helping students with their questions unless it has been demonstrated that they have attempted it. If one of my own students in Calculus I or II asked me to explain what open and closed intervals are, I would say, "No. Look it up." The only reason I chimed in on this thread is that you had been given the wrong answer. But even if I hadn't corrected Crash, it is still your responsibility to check any answers you receive here for yourself.

[Sarahisme]

if you notice what i said in my first post, i asked the question, and then stated what i thought was correct!! so its not like i didn't give it a go !

 

but i agree with what you have said,, and i will try to be more self-sufficient in future

 

Thanks Tom

[matt grime]

As ever a simple definition can be obtained by looking on wolfram

 

http://mathworld.wolfram.com/ClosedInterval.html

[Sarahisme]

thanks matt, sorry bout that guys

[matt grime]

i think at least 10% of the threads i respond to could be answered by a simple:

 

you asked about FOO, try googling for FOO+Wolfram.