The two sides that I believe are normal to the base are SDC and SCB. However, those are adjacent sides not opposite sides.
lethe: The forum posting rules and guidelines are posted for all to see, and by posting here you agree to abide by them. If you do not, your posts may be deleted. Yuriy: Check your facts. This is a privately owned forum. When you signed up as a member, you agreed to a set of conditions and rules. You also implicitly agree to abide by certain guidelines when you post in the physics forum. The owner of this site is under no obligation, legal or otherwise, to publish your writings or maintain them on the site. You maintain copyright to your writings, which means that we cannot republish them without your permission, and obviously we cannot plagiarise them. But that is a separate issue. There is no law against deleting "valuable scientific information", unfortunate as that may be.
Yuriy: Ah, I see your construction now. I was under the impression that the initial triangular pyramid was a tetrahedron. You did not make it clear that that was not the case.
No James R, there is an appropriate law, and I can explain why... The publishing my post you are establishing the priority (the date and time of the first publication) of my intellectual property. Deleting it you leave me without prove of that priority. So, you have to be careful on that issue... Either create pre-publishing censorship on matter of coincidence with Rules and separate messages before posting on public, or delight an inappropriate sentences (mark them black as it is custom in World), but do not touch whole post...
Proof of priority is your worry, not mine, Yuriy. In any case, I think you are confusing copyright law with patent law.
So which of your "rules" did I break by explaining that I've withdrawn my posts from Mac's thread, and why?
"Proof of priority is your worry, not mine, Yuriy. In any case, I think you are confusing copyright law with patent law." It would be a pleasure to meet you on the floor in court at occasion... "In any case, I think you are confusing copyright law with patent law." Good lawyer will not confuse to which Law chose to file a complain, but in Court's session any law will be used against you... But, I do not think that this "high pathetical" exchange of opinions should spoil our current good atmosphere in our Forum...
This is absurd. Dave (the guy who owns these forums) and is under no obligation to help you establish the priority of your writings. Sciforums is almost exactly analogous to a giant chalkboard that’s been left in a public place for people to use – the owner of the chalkboard has every right to erase any or all of it whenever he wishes. Securing your copyrights is your responsibility, not Dave’s.
Yuriy: I see what you mean, but you should be more careful with your language in future. I mistook 'side' for edge, where in fact you meant face.
Sorry, Nasor, but let me notice that logic (you have used the term "absurd", which is a category of Logic) and Law are "two big differences" (Russian slogan)... I do not want make here boring discussion on basics of Law, but do you know, for example, that each owner of any enterprise paying a wages (even to himself and only himself) has to keep copies of earnings and every withdrawing during ... 20 years? (If he has no such possibility, he has to send them in special State archive). Do you know that any copy of any public magazine or newspaper has to be kept forever? And so on... When you go public in any area you immediately are subject of many of laws, rules and regulations that not always are obeying ... logic... So, let us finish this discussion on the note that each of us has his own opinion on that matter... My goal was only to bring to attention of moderator that erasing information posted on public Forum a little differs from case of erasing his own writing in his own diary... From moral and judicial point of view...
Huh?? I don't get it. It looks to me that geodesic is right. If two different lines rise perpendicular to a given base, they can never intersect(as must happen if each line represents opposing sides of the same pyramid). Obviously, if two of the sides are adjacent this is possible.
contrarian, "If two different lines rise perpendicular to a given base, they can never intersect(as must happen if each line represents opposing sides of the same pyramid)" "As must" here is extra. You should say: "at least we will build a pyramid, which two opposite sides have the same line as their hights, which is perpendicular to the base" How to do that exactly is shown in my picture...
HI Yuriy! Maybe I'm just not getting this, but perhaps you can show me where my logic is wrong. Let's assume side ASD makes angle 1 with the base, ASB - ang 2, BSC ang 3, CSD ang 4. If we assume that ASD and BSC are opposing sides of a pyramid, we can also assume that angles 1 and 3 are angles of a triangle with the angle S being the angle ASD makes with BSC, being the third angle of the triangle. Since the sum of all the angles of a triangle must total 180 degrees, we know that it is impossible for both angle 1 and angle 3 to be 90(or perpendicular), this would imply that angle S is 0 or that both bases were one on top of the other.
Contrarian: The misunderstanding here is over the word sides. You and I both took side to mean an edge of the pyramid, but what Yuriy meant was face. If you look at the posted solution, the two faces ASB and CSD are normal to the base ABCD.
Thanks, geodesic. but I still do not understand your talk about "faces" and "sides". Look in this site. There you certainly see that "sides" and "base" are the "faces of pyramid". Why you think that sides was a wrong term for triangular faces of the quadrangular pyramid?
You seem to be assuming that the edges AD and BC are parallel to one another, which is not necessarily the case. Let me add some coordinates to the vertices in the diagram, maybe this will help you visualize it: S=(0,0,1) A=(1,0,0) B=(1/2,0,0) C=(0,1/2,0) D=(0,1,0) (These of course aren't the only possible co-ordinates) With these coordinates, the orignal 4-sided polyhedra in the diagram (in the top-left) would have vertices S,A,D, and the origin, (0,0,0). Then a cut is made through the plane containing B, C, and S (the top-right picture is showing this cut). ps-I think "side" is fairly common usage to describe a "face" of a polyhedra. "face" may be preferable though, since "side" is also used to mean "edge" of a polygon.
Actually if you read the copyright rules you will see that posting in public without the appropriate notice "Unpublished Work (c)- date", you can be forfieting your right to publish later.
