# Can someone help with Multivariable Limits? :D



## Forte (Sep 22, 2011)

The question is below (part (a) is what I'm stuck on). I've been doing it for a while with no real progress >_>
Most of the limits we do are just Epsilon-Delta or Squeeze Theorem, so I'm assuming this question involves one of those. (probably Squeeze Theorem)

Thanks


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## Meep (Sep 22, 2011)

Oh it's just


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## Weston (Sep 22, 2011)

There should be an "I need help with math homework" thread.

Or we can just ask meep like I always do <3


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## Hyprul 9-ty2 (Sep 22, 2011)

Which one are you stuck on?


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## Forte (Sep 22, 2011)

oya i shoulda specified >_>
Part (a) ):


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## timeless (Sep 22, 2011)

Forte said:


> oya i shoulda specified >_>
> Part (a) ):


 
is this for ap calc


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## Forte (Sep 22, 2011)

timeless said:


> is this for ap calc


 
Nope, this is Calc 3 in Uni.


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## timeless (Sep 22, 2011)

Forte said:


> Nope, this is Calc 3 in Uni.


 
oh i just started learning limits, is there a good site for tutorials?


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## Hyprul 9-ty2 (Sep 22, 2011)

*spent ages trying to figure out how to make maths look pretty on a forum*
Let me try to upload my working..


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## DaveyCow (Sep 22, 2011)

wow seems to be lots of mathy types here!
edit: me=mathy-type


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## DaveyCow (Sep 22, 2011)

Hyprul 9-ty2 said:


> *spent ages trying to figure out how to make maths look pretty on a forum*
> Let me try to upload my working..



hmmm what limit are you assuming is zero? You have to be careful when you assume somehting. It's very easy to assume what you wanna prove. If you assume what you wanna prove then you can prove anything! You can even prove that it's impossible to solve a 1x1 cube!


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## Hyprul 9-ty2 (Sep 22, 2011)

DaveyCow said:


> hmmm what limit are you assuming is zero? You have to be careful when you assume somehting. It's very easy to assume what you wanna prove. If you assume what you wanna prove then you can prove anything! You can even prove that it's impossible to solve a 1x1 cube!


 I'm just going by the assumption that what the question states is true. I let the limit of the function be 0, then I prove it using the squeeze theorem. :S?


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## Forte (Sep 22, 2011)

Jon that's so cool 

Thanks a bunch!


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## DaveyCow (Sep 22, 2011)

Hyprul 9-ty2 said:


> I'm just going by the assumption that what the question states is true. I let the limit of the function be 0, then I prove it using the squeeze theorem. :S?


 
ACK no don't assume that the limit of the function is zero! That's what you're trying to prove! If, for example, I assume that the 1x1 cube is not solvable then I can prove that it's insolvable! Proof: Assume that the 1x1 cube is insolvable. Then it follows that the 1x1 is insolvable. End of Proof. So you canNOT assume what you're trying to prove!

Of course, I could be misunderstanding what you are saying, but this is a common error among manymany undergraduates (and even graduates!) so I thought it would be worth mentioning in any case...

edit: I haven't looked through your full proof but when someone says "assume the limit is zero" and they are trying to show that "the limit is zero", that raises a red flag for me and I start questioning. So sorry if I'm speaking out of turn, but I cannot ignore the red flag!  My guess is that a prof would feel the same way....


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## Krag (Sep 22, 2011)

Hyprul 9-ty2 said:


> *spent ages trying to figure out how to make maths look pretty on a forum*


You can just use the math macro and write it in LaTeX code like \( \lim_{x,y\rightarrow0,0}A=0 \)
you just write it like [*MATH]\lim_{x,y\rightarrow0,0}A=0 [/*MATH] but without *


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## Stefan (Sep 22, 2011)

Krag said:


> you just write it like [*MATH]\lim_{x,y\rightarrow0,0}A=0 [/*MATH] but without *



noparse is another useful tag:

[noparse]\( \lim_{x,y\rightarrow0,0}A=0 \)[/noparse]


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## Hyprul 9-ty2 (Sep 22, 2011)

DaveyCow said:


> ACK no don't assume that the limit of the function is zero! That's what you're trying to prove! If, for example, I assume that the 1x1 cube is not solvable then I can prove that it's insolvable! Proof: Assume that the 1x1 cube is insolvable. Then it follows that the 1x1 is insolvable. End of Proof. So you canNOT assume what you're trying to prove!
> 
> Of course, I could be misunderstanding what you are saying, but this is a common error among manymany undergraduates (and even graduates!) so I thought it would be worth mentioning in any case...
> 
> edit: I haven't looked through your full proof but when someone says "assume the limit is zero" and they are trying to show that "the limit is zero", that raises a red flag for me and I start questioning. So sorry if I'm speaking out of turn, but I cannot ignore the red flag!  My guess is that a prof would feel the same way....


 Wouldn't it be that the squeeze theorem will only work given that you subtract the correct value of L? Then by proving the squeeze theorem works the limit must be true?.. I'm confused.


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## DaveyCow (Sep 22, 2011)

For what it's worth, here's how I would have written up 3a (really just what hyprul did, but explained differently).


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## ben1996123 (Sep 22, 2011)

Thompson said:


> im in grade 10





Spoiler











Couldn't resist lol.

On topic: I am no understand what is on about.


Edit:




Stefan said:


> noparse is another useful tag:
> 
> [noparse]\( \lim_{x,y\rightarrow0,0}A=0 \)[/noparse]


 
I've wondered for a while why people don't know about noparse.

[noparse][noparse]\( noparse makes tags die \)[/noparse][/noparse].


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## tozies24 (Sep 23, 2011)

DaveyCow said:


> no don't assume that the limit of the function is zero! That's what you're trying to prove!



_Claim _that the limit of the function is zero and then use logical steps to get to the answer. All of his work is correct, its just that he used poor wording at the top.


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## Keroma12 (Sep 23, 2011)

Forte said:


> Nope, this is Calc 3 in Uni.


 
The advanced version or the regular version?


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## Hyprul 9-ty2 (Sep 23, 2011)

tozies24 said:


> _Claim _that the limit of the function is zero and then use logical steps to get to the answer. All of his work is correct, its just that he used poor wording at the top.


 Oh :S. I actually had a lot more stuff up there, but it wouldn't fit in the picture, so I just took the "important" bits.


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