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#26 Re: Help Me ! » sequence question » 2010-09-12 16:19:14

nha

Thanks bobbym and soroban. I feel stupid now, I didn't know how complicated the functions were. I really just want to find a pattern so I can find the next 2 numbers in each sequence.

I got it for the first:
0+0+1=1
0+1+1=2
1+1+2=4
1+2+4=7
2+4+7=13
4+7+13=24

7+13+24=44
13+24+44=81

But the second I can't seem to get. That 19 is my issue.

Thanks again, and sorry for having you finding the function, I didn't think they would be so big and difficult.

#27 Help Me ! » sequence question » 2010-09-11 23:34:47

nha
Replies: 15

Hey everyone, I have a simple question.

How can I find a formula for the following sequences (like in the form ((n+1)n)/2 etc):

0,0,1,1,2,4,7,13,24

and

2,1,3,4,7,11,19,30


Thanks

#28 Re: Help Me ! » triple integral » 2010-09-10 16:21:47

nha

Don't worry about it, I give up. I must have written it wrong. Sorry for wasting your time all.

#29 Re: Help Me ! » triple integral » 2010-09-10 15:52:59

nha

If it doesn't look like it can be solved I must have written it out wrong.

#30 Re: Help Me ! » triple integral » 2010-09-10 15:47:45

nha
bobbym wrote:

Hi;

What textbook, do you remember?

Nah, from a while back but I wrote out the question in my book. Might have been stewarts.

EDIT: would converting to polars work?

#31 Re: Help Me ! » triple integral » 2010-09-10 15:43:41

nha
bobbym wrote:

Hi nha;

Why are you certain this one can be done?

It is a textbook question.

#32 Re: Help Me ! » triple integral » 2010-09-10 15:41:21

nha
George,Y wrote:

Could you just change the integration order to
y->x->z ?

I just tried that and it wont work, I get an integral that the calculator wont even do,

I think a different coordinate system needs to be used, but I still can't get it.

#33 Help Me ! » triple integral » 2010-09-09 21:55:20

nha
Replies: 12

Hey everyone yet again, I have a really hard triple integral that I need help on.


My working:

But then to integrate with respect to y is very tricky for me, I can get it by calc but it is big and I want to know how to do it by hand.

Any help would be nice.

Thanks

#34 Re: Help Me ! » equivalence relation questions » 2010-09-06 11:24:46

nha
bob bundy wrote:

hi nha,

Not my best subject but, as no one else is posting I'll throw in my ideas.

(ii) first.  I think you've got to show symmetric, reflexive and transitive. 

So, for example, define R so that a R b. when a and b are both in Si. 

As  a in Si and b in Si => b in Si and a in Si => b R a so it is reflexive.

(i)  ??? What ordered pairs is this question after?  I really cannot get this.  Sorry.  Do you have a given example already to show what this means?

Bob

Hi Bob, for Q2 I still don't understand, could you explain it a bit more. For Q1, that is all the question gives, that is why I don't understand it either.

#35 Help Me ! » equivalence relation questions » 2010-09-05 20:28:32

nha
Replies: 4

Hi everyone again, I am doing alot of math questions today have keep running into some problems here and there.

It would be great if anyone could help me with a couple of questions relating to equivalence relations.

Q1) Write down the ordered pairs corresponding to the equivalence relation, which yields the partition:
{a,c,e,g,j},{f},{b,d,h},{i}

Q2) Let {S_i}_i be a partition of a set S, i.e.

with
if
. Prove that this partition {S_i}_i gives rise to an equivalence relation on S.


My textbook doesn't give me much help with these, any help would be nice. Thanks

#36 Re: Help Me ! » Catalan number help » 2010-09-05 20:11:58

nha

Ah yes, thanks again bobbym. I see why I couldn't get it right.

#37 Re: Help Me ! » Catalan number help » 2010-09-05 19:30:14

nha
bobbym wrote:

Hi nha;

I am not following you here. To get the n th Catalan Number you just plug into that poor approximation.

There is an exact formula for Catalan numbers and a generating function.

Are you trying to prove  that the ratio of that approximation to the n th Catalan number approaches 1 as n->∞?
That is what you need stirlings approximation for.

lol, I must have deleted "Prove that for m very large".

The question is:
Prove that for m very large

#38 Help Me ! » Catalan number help » 2010-09-05 18:29:27

nha
Replies: 5

Hey everyone, I need some more help dealing with Catalan number function.

where

denotes the
-Catalan number.



I know I need to use Stirling's estimate:

for integers
and the limit definition of
, but I just can't seem to make anything of it.

Thanks to anyone that helps.

#39 Re: Help Me ! » Optimal Design question » 2010-09-05 18:01:05

nha
bobbym wrote:

Hi nha;

Your welcome, for Q2, I am not sure that I understand the question.

I think it is asking to find the n-gon that has the largest area inscribed in the circle, but it would have to be an answer like 'the regular n-gon' otherwise it doesn't make sense to me. Maybe because as n gets larger, a regualr n-gon approximates to a circle??

#40 Re: Help Me ! » Optimal Design question » 2010-09-05 17:52:55

nha

Thanks so much bobbym. It seems so easy now, thanks for the huge help. I proved it was a maximum.

Any thoughts/help on Q2? I believe it should be a regular n-gon but I don't know how to go about proving this.

#41 Help Me ! » Optimal Design question » 2010-09-05 15:12:05

nha
Replies: 5

Hello math lovers, can someone please provide me some help with an optimal design question. Any sort of help would be awesome.

Q1) Show that among all the 4-sided polygons inscribed in a circle the squares have the largest area.
Q2) And for fixed n which is the n-gon of largest area inscribed in a circle?

For Q1 I know I should focus on showing that all sides of a quadrilateral of maximal area have to be of equal length. So I would use Brahmagupta's formula I think, but how would I show that the squares have the largest area?

Q2) I don't know how to approach this. sad


Thank you all for any help. smile

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