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Tzetze DUMB from a converted church in Venice, Italy Since: Jan, 2001
DUMB
#726: Dec 16th 2010 at 9:53:23 AM

Yeah, I've read tons of professional essays which use the first person.

Anyway, this isn't homework, but could somebody versed in symbolic logic help me stop driving myself crazy

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Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#727: Dec 16th 2010 at 1:07:18 PM

...what the heck is M tongue

Tzetze DUMB from a converted church in Venice, Italy Since: Jan, 2001
DUMB
#728: Dec 16th 2010 at 1:12:51 PM

Either a typo or anything. They pulled that a few times in the homework, making you prove arbitrary statements from contradictions.

I'm not sure whether I'd prefer the professor to have messed up the question, or me to be stupid...

[1] This facsimile operated in part by synAC.
Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#729: Dec 16th 2010 at 1:16:52 PM

So basically you could prove ~M if the first two are internally inconsistent?

Taelor Don't Forget To Smile from The Paths of Spite Since: Jul, 2009
Don't Forget To Smile
#730: Dec 16th 2010 at 1:20:10 PM

Stylistic things like that are generally there for a reason, and breaking them can make it not really an essay anymore.
This is completely true. However, the reason that stylistic rules exist is because, in the majority of cases, they tend to make the essay more readable. In some cases, though, they do not; and in these cases, should be abandoned. The purpose of an essay is to convey a message to the reader — any rule that expedites this should be followed, and any rule that does not, should not. When writing, remember that stylistic rules only exist aposteriori, not apriori, and ask yourself not whether a something follows a rule, but whether it will facilitate you're final goal — expressing yourself.

The Philosopher-King Paradox
Tzetze DUMB from a converted church in Venice, Italy Since: Jan, 2001
DUMB
#731: Dec 16th 2010 at 1:27:49 PM

So basically you could prove ~M if the first two are internally inconsistent?

Yeah. There's an example in the Wikipedia article; it goes

  1. Lemons are yellow and lemons are not yellow.
  2. From 1, lemons are yellow.
  3. From 2, lemons are yellow or Santa Claus exists  *.
  4. But from 1, lemons are not yellow.
  5. So from 3 and 4, Santa Claus must exist.

Logic's weird.

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Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#732: Dec 16th 2010 at 1:39:56 PM

Honestly I'm not even seeing how you prove G from that. I truth tabled it out, and two of the three J,G,Q sets that evaluate both constraints to true use G=false.

Tzetze DUMB from a converted church in Venice, Italy Since: Jan, 2001
DUMB
#733: Dec 16th 2010 at 1:41:57 PM

I can write it out, wait a sec.

..wait, did you seriously do a truth table for four variables? Why

  1. (F⊃J)⊃(G⊃Q)
  2. J•~Q
  3. J [2, simp]
  4. J∨~F [3, add]
  5. ~F∨J [4, comm]
  6. F⊃J [5, mat imp]
  7. G⊃Q [1, 6, MP]
  8. ~Q [2, simp]
  9. G [7, 8, MT]

edited 16th Dec '10 1:44:38 PM by Tzetze

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Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#734: Dec 16th 2010 at 1:48:36 PM

Nevermind, I'm an ass, I got a solid value on G when I expanded into boolean terms. I was accidentally replacing (J && !Q) with (J == !Q).

It's only 16 lines dude :P

edited 16th Dec '10 1:59:38 PM by Pykrete

Tzetze DUMB from a converted church in Venice, Italy Since: Jan, 2001
DUMB
#735: Dec 16th 2010 at 1:50:52 PM

I know, but... so tedious!

When I bitched about it before Nornagest mentioned doing one for six variables or something. -_____-

Well, in any case, this has reassured me that I did more or less know what I was doing.

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Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#736: Dec 16th 2010 at 2:03:42 PM

Wait.

7) G⊃Q [1, 6, MP]
8) ~Q [2, simp]
9) G [7, 8, MT]

Wouldn't that last step show ~G instead of G? If you need G⊃Q and Q=F, G⊃F forces ~G.

Either way, there's no contradiction for an explosion.

edited 16th Dec '10 2:07:28 PM by Pykrete

Tzetze DUMB from a converted church in Venice, Italy Since: Jan, 2001
DUMB
#737: Dec 16th 2010 at 2:07:54 PM

Oh yeah, so it does. Brainfart! ^_^; I didn't do that on the final, though.

Huh, I wonder what happens if he really did make a mistake... after staring at it up to ~G for half an hour I just wrote out «It's impossible to use the principle of explosion to prove an unrelated proposition, because there is no contradiction in the premises.» Hopefully that's well thought out enough to get whatever.

[1] This facsimile operated in part by synAC.
LoniJay from Australia Since: Dec, 2009 Relationship Status: Pining for the fjords
#738: Dec 16th 2010 at 2:44:01 PM

Huh. I had it drummed into me in highschool that you do not use I in an essay ever. Oh well.

Be not afraid...
Barcode711 Clutch pedal = sidestep from Uddiyana Since: Apr, 2009
Clutch pedal = sidestep
#739: Dec 18th 2010 at 9:02:46 PM

Math question. "Contour" integrals. Complex numbers. (These integrals are probably named different things in different areas, I think, so don't get scared as long as you already know what integrals are.)

Bonus question - why did I have to check if the points were along the path when it was regular complex integrals, but they don't have to be when it's these other integrals?

I am expecting that |z| = 16 will become (x1 = -16, x2 = 16) and (y1 = -16, y2 = 16), but that just seems a little suspect to me.

EDIT: Solved this on my own, but I still don't know if my converseion of C to R was correct. (die)q/(die)x- (die)p/(die)y = 0, integration results in C (constant), C - C (due to range integral) = 0. Repeat for y. Still get 0.

EDIT: Got my answer to that too.

edited 18th Dec '10 10:24:37 PM by Barcode711

Worshipper of Ahura Mazda, as proclaimed by Zoroadster http://twitter.com/bpglobalpr
Noaqiyeum we must dissent (it/they) from across the gulf of space (Time Abyss) Relationship Status: Arm chopping is not a love language!
we must dissent (it/they)
#740: Jan 7th 2011 at 2:56:58 PM

A container is supported by three cables. The maximum allowable tension in any of the cables is 460 N. What is the maximum weight of the container?

All three cables are attached to the container at A = (0, -.60, 0); the other ends are at B = (.45, 0, 0), C = (0, 0, -.32), and D = (-.50, 0, .36). Assume massless straight cable, etc.

I'm trying to calculate the fractions in which any weight is distributed between the three cables in order to determine which experiences the greatest tension, then simply substitute 460 N into the force on the weakest cable; however, while I'm reasonably sure the weakest cable is AD due to the acuter angle of attachment, I haven't managed either to prove it yet, or even to relate the cable strengths to each other beyond the obvious (Only cables AB and AD have an x-component to their tension vectors, so they must be of equal magnitude in that direction, and the same goes for AC and AD along the z-axis).

I feel as though either there's something blatant that I'm missing, or I'm simply overthinking the problem and trying to solve it the wrong way. tongue

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Deboss I see the Awesomeness. from Awesomeville Texas Since: Aug, 2009
I see the Awesomeness.
#741: Jan 7th 2011 at 3:18:46 PM

Was there a picture? I'm having trouble picturing this.

Fight smart, not fair.
Noaqiyeum we must dissent (it/they) from across the gulf of space (Time Abyss) Relationship Status: Arm chopping is not a love language!
we must dissent (it/they)
#742: Jan 7th 2011 at 3:48:17 PM

There was, but nothing I didn't describe... Imagine three cables bolted irregularly into the ceiling at points B, C, and D, with the hanging ends joining together to suspend a bucket at point A.

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KylerThatch literary masochist Since: Jan, 2001
literary masochist
#743: Jan 7th 2011 at 4:10:03 PM

The tension of the cables on the container can be divided into two components, one parallel to the y-axis, the other parallel to the xz-plane (the ceiling). Now, since the container isn't moving (implying that acceleration is zero), we can assume that there is no net force acting on it. There's gravity, but it's being canceled out by the net force of the tension of the cables on the box, which should be completely vertical.

Which means that the sum of the components parallel to the xz-plane should equal to zero. From there, it's a matter of deriving their magnitudes, since you already know their directions.

You could try three test cases where you max out the tension for one cable, and check whether any of the other two cables exceed the limit for that case... I think. I'm not entirely sure about this part.

This "faculty lot" you speak of sounds like a place of great power...
Deboss I see the Awesomeness. from Awesomeville Texas Since: Aug, 2009
I see the Awesomeness.
#744: Jan 7th 2011 at 5:18:41 PM

Ah, now I get it. It's centered at the origin and then dropped, okay. I couldn't figure out the reason for giving the anchor a position. Yeah, AD is going to be the weakest point, because it's got the longest cable.

Fight smart, not fair.
Madrugada Since: Jan, 2001
#745: Jan 7th 2011 at 5:27:47 PM

If you have to take into account it being dropped, won't the shortest cable be the one that is most likely to fail? It's the one that will be holding all the weight for however long it takes for the second-longest-one to start doing its share?

Deboss I see the Awesomeness. from Awesomeville Texas Since: Aug, 2009
I see the Awesomeness.
#746: Jan 7th 2011 at 5:53:44 PM

It's not being dropped, it's being weighted.

Fight smart, not fair.
Madrugada Since: Jan, 2001
Pykrete NOT THE BEES from Viridian Forest Since: Sep, 2009
NOT THE BEES
#748: Jan 7th 2011 at 6:50:31 PM

I'm getting AD as the highest-tension one too, albeit not by much.

Also I got screwed up at first because I'm used to my engineering problems using Z as up instead of Y. tongue

edited 7th Jan '11 6:51:32 PM by Pykrete

Noaqiyeum we must dissent (it/they) from across the gulf of space (Time Abyss) Relationship Status: Arm chopping is not a love language!
we must dissent (it/they)
#749: Jan 8th 2011 at 1:31:14 PM

Okay... I'm still stuck about how to calculate the relative tensions on the cables, though.

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Deboss I see the Awesomeness. from Awesomeville Texas Since: Aug, 2009
I see the Awesomeness.
#750: Jan 8th 2011 at 9:19:04 PM

Calculate the triangular angles so that you have the force balance. Then you add in the vertical thing. I think that's related to what you're trying to do, I've got a pounding headache and I'm not sure.

Fight smart, not fair.

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