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Artnotwar
Chemical Researcher


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Simple geometry question
#21958959 - 07/18/15 01:03 AM (8 years, 6 months ago) |
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I'm trying to draw a circle and divide it into three segments with only a compass and using no measurements.
I want the segments to be divided by parallel chords, each chord at ⅓ of the diameter.
Can anyone tell me how I can achieve this? Is it possible without using measurements?
-------------------- -------------------------------------------------------------------------------- Until the 20th century, reality was everything humans could touch, smell, see, and hear. Since the initial publication of the charged electromagnetic spectrum, humans learned that what they can touch, smell, see, and hear... is less than one millionth of reality. --------------------------------
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I_was_the_walrus
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Re: Simple geometry question [Re: Artnotwar]
#21958981 - 07/18/15 01:15 AM (8 years, 6 months ago) |
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Maybe if you explained it more clearly. You want the circle divided into 3 parallel sections, as in 3 horizontal sections on top of eachother?
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starfire_xes
I Am 'They'



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Re: Simple geometry question [Re: Artnotwar]
#21958986 - 07/18/15 01:17 AM (8 years, 6 months ago) |
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C=pi*d C/(3*pi) = d/3 2*pi = 360 degrees (radians to degrees)
You should be able to calculate the angles from that.
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koods
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A math class wants you to use an imprecise device to accomplish this?
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koods
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Re: Simple geometry question [Re: koods]
#21959011 - 07/18/15 01:29 AM (8 years, 6 months ago) |
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Ah wait. Divide the circle into half horizontally. Ok draw two circles with the focus being the outsides of the circle where the bottom half meets the top half. The circles have a diameter of 1/3 the full circle. Draw two parallel lines from the tops of the circles and the bottoms.
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NotSheekle said “if I believed she was 16 I would become unattracted to her”
Edited by koods (07/18/15 01:32 AM)
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Shroomslip
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Re: Simple geometry question [Re: koods]
#21959081 - 07/18/15 02:18 AM (8 years, 6 months ago) |
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I'm assuming it needs to be pretty accurate, with no measurement how are you going to determine what is 1/3rd the size of the original circle?
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With my face against the floor I can’t see who knocked me out of the way. I don’t want to get back up but I have to so it might as well be today. Nothing appeals to me no one feels like me, I’m too busy being calm to disappear. I’m in no shape to be alone contrary to the shit that you might hear. You can't wake up, this is not a dream. You're part of a machine, you are not a human being With your face all made up, living on a screen. Low on self esteem, so you run on gasoline
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akira_akuma
Φύσις κρύπτεσθαι ὕψιστος φιλεῖ

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Re: Simple geometry question [Re: koods] 2
#21959085 - 07/18/15 02:19 AM (8 years, 6 months ago) |
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Quote:
koods said:

those are just two penis's playing swords.
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I_was_the_walrus
eggshells



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Re: Simple geometry question [Re: akira_akuma]
#21959092 - 07/18/15 02:24 AM (8 years, 6 months ago) |
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Here we go again..
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akira_akuma
Φύσις κρύπτεσθαι ὕψιστος φιλεῖ

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koods explained it pretty clearly, though, he and Star should be commended.
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koods
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Not everything is a dick pic
Somethings are two dicks pics
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NotSheekle said “if I believed she was 16 I would become unattracted to her”
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Shroomslip
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Re: Simple geometry question [Re: Artnotwar]
#21959103 - 07/18/15 02:29 AM (8 years, 6 months ago) |
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1. Draw perfect cricle on paper. 2. Fold paper in half so that the halves are exactly on top of each other but also so the edges of the paper that run perpendicular to the fold are exact. 3. Using edges of the paper as a guide, fold both halves of the circle so the two highest points of the the sections meet touch.
Kinda cheated, didn't find that answer exactly but something I saw while trying to look it up sparked the idea.
Damnit nevermind that would give 4ths.
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With my face against the floor I can’t see who knocked me out of the way. I don’t want to get back up but I have to so it might as well be today. Nothing appeals to me no one feels like me, I’m too busy being calm to disappear. I’m in no shape to be alone contrary to the shit that you might hear. You can't wake up, this is not a dream. You're part of a machine, you are not a human being With your face all made up, living on a screen. Low on self esteem, so you run on gasoline
Edited by Shroomslip (07/18/15 02:31 AM)
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KremrBigSikter
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Re: Simple geometry question [Re: Shroomslip]
#21959123 - 07/18/15 02:37 AM (8 years, 6 months ago) |
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-------------------- I have pneumonia
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koods
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Good solution, but for geometry class? Maybe arts and crafts.
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NotSheekle said “if I believed she was 16 I would become unattracted to her”
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akira_akuma
Φύσις κρύπτεσθαι ὕψιστος φιλεῖ

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Re: Simple geometry question [Re: koods]
#21959139 - 07/18/15 02:46 AM (8 years, 6 months ago) |
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draw a circle, tie a bow out some moustached guy's nosehair, flatten pancakes into 3D. got it.
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Gorlax



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Re: Simple geometry question [Re: akira_akuma]
#21959405 - 07/18/15 06:11 AM (8 years, 6 months ago) |
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It's north korea's death camp test. lawlz
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Mr.GuessWork
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Re: Simple geometry question [Re: koods]
#21959682 - 07/18/15 08:45 AM (8 years, 6 months ago) |
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Quote:
koods said: Ah wait. Divide the circle into half horizontally. Ok draw two circles with the focus being the outsides of the circle where the bottom half meets the top half. The circles have a diameter of 1/3 the full circle. Draw two parallel lines from the tops of the circles and the bottoms.

I don't think this works. The length of the chord would have to be the same as the diameter of those circles, and I don't think it is. I have no idea how to solve this either. I think it needs some advanced circle skills. My geometry education was focused on polygons . Fuck it. I'll try anyway.
I felt lazy, so I halfassed together a tedious solution that's impractical, but it works. You can always use a strait-edge (I assume it's allowed, otherwise tedium increases) and a compass to divide a line in half. If you successively divide the diameter of the circles by 2, eventually you get a radius that is 1/32 the original radius. I know that's a bitch, but now you can string together 8 of those 1/32 lines to get a line that's 1/3 the radius of the original circle. Redraw the original circle with a diameter line and use the 1/3 radius-line to calibrate the compass. Find the point on the diameter line where a new 1/3 diameter circle will intersect with the big circle at a right angle and draw the chord there. Repeat that last bit for the other side of the circle, and you'll have two parallel chords that are 1/3 the diameter of the circle. You should start with a pretty big circle.
EDIT: 1/32 is the earliest power of 1/2 in the sequence that can be multiplied by a whole number to get 1/3. That's why I was forced to pick it.
Edited by Mr.GuessWork (07/18/15 08:50 AM)
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Mr.GuessWork
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Quote:
starfire_xes said: C=pi*d C/(3*pi) = d/3 2*pi = 360 degrees (radians to degrees)
You should be able to calculate the angles from that.
I tried to figure it out with trig, but you end up with irrational angles that would be impossible to create with just a compass. We're basically stuck with solutions that use rational numbers.
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PLURAL
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Bro, 8/32 is 1/4, not 1/3.
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psi
TOAST N' JAM


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Quote:
Mr.GuessWork said: EDIT: 1/32 is the earliest power of 1/2 in the sequence that can be multiplied by a whole number to get 1/3. That's why I was forced to pick it.
Wait, what? I'm pretty sure there is no power of 1/2 that can be multiplied by a whole number to give 1/3 (since 3 is not a factor of any power of 2.)
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Mr.GuessWork
Stranger

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Re: Simple geometry question [Re: psi]
#21959754 - 07/18/15 09:20 AM (8 years, 6 months ago) |
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Aw fuck. You're right. I Can't believe I messed that up  . So we need some way to get thirds with a compass.
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Mr.GuessWork
Stranger

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http://www.mathopenref.com/constdividesegment.html
Here's a step by step thing that shows how to get an arbitrary number of division of a line. That last fuckup still hurts.
Edited by Mr.GuessWork (07/18/15 09:24 AM)
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psi
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Re: Simple geometry question [Re: koods]
#21959765 - 07/18/15 09:25 AM (8 years, 6 months ago) |
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Quote:
koods said: A math class wants you to use an imprecise device to accomplish this?
From what I understand, geometry proofs can often involve demonstrating how one might construct something with a compass and straightedge. I'm pretty clueless in this area though. At first I thought OP was trolling us with some impossible task, but it turned out I was thinking of trisecting an angle. Apparently it's been proven that it's impossible to trisect an arbitrary angle with a compass and straightedge.
This vid apparently shows how to trisect a line segment. If you knew how to construct a square around the circle (and the video is legit) then you could do this on the top and bottom of the square and then connect them. Like I say though I barely know the first thing about this stuff.
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Mr.GuessWork
Stranger

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Re: Simple geometry question [Re: psi]
#21959780 - 07/18/15 09:30 AM (8 years, 6 months ago) |
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Quote:
psi said:
Quote:
koods said: A math class wants you to use an imprecise device to accomplish this?
From what I understand, geometry proofs can often involve demonstrating how one might construct something with a compass and straightedge. I'm pretty clueless in this area though. At first I thought OP was trolling us with some impossible task, but it turned out I was thinking of trisecting an angle. Apparently it's been proven that it's impossible to trisect an arbitrary angle with a compass and straightedge.
This vid apparently shows how to trisect a line segment. If you knew how to construct a square around the circle (and the video is legit) then you could do this on the top and bottom of the square and then connect them. Like I say though I barely know the first thing about this stuff.
I thought he was trolling us at first too, then I realized that I'd never used a compass for anything in geometry, and my entire education on compasses was basically somebody mentioning that trisecting an angle and the squaring of a circle were impossible. I guess it's not a hot topic in most geometry classes. They tend to focus on pre-trig stuff I think.
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psi
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Yeah I took a high school geometry class that covered vectors and projections and so on but nothing on this classical geometry stuff. My sister's boyfriend does math tutoring and he was showing me this iPad app for learning to do these construction style proofs.
I need a bunch of math for the degree I'm working on (computer science) but I've mostly been avoiding the math classes I need. I used to be pretty good in math in high school but I kind of lost my touch after a decade out of school. It's getting to the point where I have to do the math and stats stuff to get into the CS courses I want to take though.
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starfire_xes
I Am 'They'



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Re: Simple geometry question [Re: psi]
#21959803 - 07/18/15 09:42 AM (8 years, 6 months ago) |
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You can either algebraically find the angle of rotation from the center as i said earlier, or draw arcs with the compass that pass through the midpoint of a radial line drawn to the center and the edge of the circle to find the points.
Connecting algebra to the geometry is called analytic geometry. But I guess this was supposed to be a compass proof?
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    [/url] [/url]
IF THE NEIGHBORS COMPLAIN BECAUSE THE MUSIC'S TOO LOUD, TURN IT UP SO YOU CAN'T HEAR THEM BITCH
Edited by starfire_xes (07/18/15 09:47 AM)
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Prisoner#1
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Re: Simple geometry question [Re: koods] 1
#21959811 - 07/18/15 09:45 AM (8 years, 6 months ago) |
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Quote:
koods said: Ah wait. Divide the circle into half horizontally. Ok draw two circles with the focus being the outsides of the circle where the bottom half meets the top half. The circles have a diameter of 1/3 the full circle. Draw two parallel lines from the tops of the circles and the bottoms.

did you just draw a picture of a bug and tell him that's the solution
epic work man!
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