x Turn on thread page Beta
 You are Here: Home >< Maths

# Mega A Level Maths Thread - Mark V watch

1. (Original post by RoseGatz)
Got a question I'm a bit stuck on, care to help Zacken or anyone else for that matter? It's more pure stuff

The function is defined by

where

Show that as

I've managed to show that instead of showing , got no idea where the minus is coming from.
Impressive !

but in the negative sense, if you get me?

Look at the graph of for to see why diverges to .

Although to be fair - if you have a limit that equals either plus or minus infinity, it's pretty much the same thing in that the limit does not exist.
2. (Original post by Zacken)
Impressive !

but in the negative sense, if you get me?

Look at the graph of for to see why diverges to
Haha I know right! Took me a while to get the hang of it.

We went through this is class earlier today, we knew it was obviously considering the graph but is this just an assumption we make? Is there no way to explicitly get or do we just go off assumption because of the graph?

(Original post by Zacken)
Although to be fair - if you have a limit that equals either plus or minus infinity, it's pretty much the same thing in that the limit does not exist.
3. (Original post by RoseGatz)
Haha I know right! Took me a while to get the hang of it.

We went through this is class earlier today, we knew it was obviously considering the graph but is this just an assumption we make? Is there no way to explicitly get or do we just go off assumption because of the graph?
Saying that is a shorthand way of saying that the limit doesn't exist, i.e: that it diverges. Having anything nearly almost always never makes sense. So fussing about whether it's plus or minus infinity is something that we don't really tend to do because in either case - we're still just saying that the limit doesn't exist.

If you want some justification for why , you could try looking at , might work - I haven't thought about it properly though, I'm rushing this out.

Most of the things you do with limits is based on epsilon-delta proofs, that is, the formal condition for limits and once you start working with infinity in there, that falls apart because you can't have something converge to infinity - so at this level, you're reduced to looking at graphs and making assumptions instead of working with things like you would in a real analysis course.

This: http://math.stackexchange.com/questi...nity-not-exist may shed some light on what I meant.
4. Isn't the x^3 responsible for its divergence to -infinity, since as x approaches 0 ln(x) becomes large and negative therefore making the fraction small and negative?
5. (Original post by drandy76)
Isn't the x^3 responsible for its divergence to -infinity, since as x approaches 0 ln(x) becomes large and negative therefore making the fraction small and negative?
is what causes the divergence to infinity. is what causes the divergence to . The user is enquiring as to the negative sign.
6. (Original post by Zacken)
is what causes the divergence to infinity. is what causes the divergence to . The user is enquiring as to the negative sign.

Turn on thread page Beta
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 22, 2016
Today on TSR

### Loughborough better than Cambridge

Loughborough at number one

Poll
Useful resources

## Make your revision easier

Can you help? Study help unanswered threadsStudy Help rules and posting guidelinesLaTex guide for writing equations on TSR

## Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE