need help with the following qns (Speechless)

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- Sep 23rd 2010, 09:28 AMtionghow to calculate the number of grid lines within a circle?
need help with the following qns (Speechless)

http://img210.imageshack.us/img210/5...reenshothc.png - Sep 23rd 2010, 09:34 AMTraveller
Observe that what you are looking for is the number of grid-lines inside the square circumscribing the circle, with its sides parallel to the axis. Can you do it now ?

- Sep 23rd 2010, 10:24 AMtiong
- Sep 23rd 2010, 10:56 AMTraveller
Yes, the problem asks you to count the lines including those that are partially covered.

- Sep 24th 2010, 12:36 AMtiongIs there any existing math formula that can describe this concept?
- Sep 24th 2010, 12:41 AMtiong
- Sep 24th 2010, 01:21 AMWilmer
But then you're not counting the "number of lines"; instead you're "measuring" cut off portion of lines.

Seems like a useless task, like if some lines are cut off at the 3/4 point, this leaves a 1/4 line inside

circle, so 4 of those make up a line? I suggest you clarify this... - Sep 24th 2010, 05:36 AMtiong
---Quote (Originally by tiong)---

need help with the following qns (Speechless)

Image: http://img210.imageshack.us/img210/5...reenshothc.png

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The number of line segments within the circle is 2(1)+2(1) initially.

Then if you double the number of lines, you get 4(3)+4(3).

If you double again, you get 8(7)+8(7).

If you keep doubling, the number of segments (irrespective of length) is 2^n\left(2^n-1\right)

Similarly, the number of segments in the external square is (5)\left(2^{n-1}\right)(5)\left(2^{n-1}+1\right)

You could express this as a ratio and if you take the limit as n goes to infinity,

you will get the ratio of the area of a 2x2 square to the area of a 5x5 square,

since the formula doesn't take into consideration the varying line segment lengths.

I doubt if that's the purpose of the question.

Does the question have anything to do with {\pi} ?

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to Archie Meade who replied but somehow your post is gone

ya, when the number of gird lines goes to inifinity,

the ratio suppose to be area of the circle over overall area, which is (pie*(sqrt))/x*y

actually what im trying to prove is as the no of grid lines increases within the same area, the ratio of the area covered by the circle over the overall area increases as well

wondering if there any existing math formula that have similiar density concept? - Sep 24th 2010, 07:43 AMtiong
Hi, actually this qns is needed to explain my network project stuff, but i didn't go into that because it will become irrelevant in this math forum, basically i need to count the number of lines regardless whether they are full or partial length, so wondering is there a way to count it or do i have to roughly estimate like what u mention?

- Sep 24th 2010, 07:51 AMWilmer
You are not answering our questions, plus contradicting yourself:

you said earlier:

"thanks, but is there a way to count those partially covered lines as .X of the line?"

now you're saying:

"i need to count the number of lines regardless whether they are full or partial length"

I leave you in travellers' hands... - Sep 24th 2010, 07:56 AMtiong
hi, i think phrased my sentence ""i need to count the number of lines regardless whether they are full or partial length" wrongly sry,

what i mean is if its a full length line i need to count it as 1, if the line has only 2/3 of it within the circle, i have to count it as 2/3. - Sep 24th 2010, 09:33 AMWilmer
- Sep 24th 2010, 11:10 AMTraveller
You have already written about the solution when n approaches infinity. I don't think that there is any closed form for the expression for a given n. If there are n-1 equally spaced lines in between each line in the original grid, the formula will look like:

$\displaystyle

\frac {2 + 4(\frac{1}{n}( \sum_{k=1}^{n}\sqrt{(n^2 - k^2)}) }{ 5( 5n + 1) }$