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I did suspect once that PowerOfPi at AoPS was the same as LuisRodg over here because they had the same avatar; now Im not so sure.
Because its graph lies completely above the x-axis and does not intersect it.
2) Hint: Does
have a multiplicative identity?Whats the problem?
Im getting a picture of probability density function in quantum mechanics here.
To generalize:
If S and T are two sets of four teachers and Q_S = Q_T then we must have S = T since S is the set of teachers who don't have the answer to Q_S and T is the set of teachers who don't have the answer to Q_T. Therefore we must have at least as many questions are there are sets of four teachers.
To elaborate, the condition that no four (or fewer) teachers know all the answers means that if
are four teachers, there is an answer such that none of dont have . Now, suppose that are are distinct sets of four teachers such that there is an answer such that dont have and dont have the same answer . Since the sets of four are distinct, there is some such that . But if dont have , then the other six teachers must have (since every answer must be given to (at least) six teachers) and is one of these six teachers! Contradiction! Therefore, given distinct sets of four teachers, there must be distinct answers which they dont have. Hence the total number of answers must be at least the total number of selections of four teachers, i.e. .Thanks Avon! Youre a genius.
Your image file cant be found but I found the same post by you on another forum; this is Christopher Heckmans ASCII recreation of your diagram on www.mathkb.com.
+--+--+--+--+--+
| | | |x1| |
+--+--+--+--+--+
| | | |x2| O|
+--+--+--+--+--+
| |x3| | | |
+--+--+--+--+--+
| | | | | |
+--+--+--+--+--+
|x4| | |x5| |
+--+--+--+--+--+
My gut feeling is that it cant be done but unfortunately I dont have a proof.
Well, unless I see a counterexample, I will stick to 210 as the answer.
I was thinking "level 3 of Cubilius" is Impossible I think there's a flaw in that game!
NO THERE ISNT!!
Here is a smaller example to illustrate my point.
Teacher 1: {1,2,3,4,5,6}
Teacher 2: {1,2,3,7,8,9}
Teacher 3: {1,4,5,7,8,10}
Teacher 4: {2,4,6,7,9,10}
Teacher 5: {3,5,6,8,9,10}
Thus no two teachers have the complete set but any three teachers do. Again 10 may not be the minimum answer, but, as you can see for yourself, it works.
Well, I can only say that the answer must be less than or equal to 210. This is my proof.
Thus, if there are
questions, we can arrange things so that given any four teachers, there will be (exactly) one answer which is not given to these four and so they will not have the complete set. On the other hand any five teachers will have the complete set. If not, it would mean that one answer has not been given to these five teachers but we have already given every answer to six teachers so this cannot arise.If 210 is the answer, then each teacher will have
questions. However I cant prove that 210 is actually the minimum number; all Ive proved is that 210 works.xy'-y=0 (or, if you prefer: x(dx/dy)-y=0)
The way I do it is to solve the differential equation (by separating the variables and integrating) getting the general solution
. Hence the solution family is the set of all nonvertical straight lines through the origin, so is the common point you are looking for.Consider the list
. Each is an even permutation, being a product of two odd permutations. They are also distinct, for by the cancellation law we have . Hence there are at least even permutations.Conversely, if
is an even permutation, then is an odd permutation and so is one of the permutations . Hence is one of the permutations .From this, we conclude that there are exactly
even permutations, i.e. there are as many odd permutations as even ones.Or your route could be like this:
[align=center]http://www.mathsisfun.com/graph/functio … =-2&ymax=2[/align]
In which case the IVT applies but Rolles theorem does not!
Rolles theorem requires the curve to be differentiable (i.e. smooth) not just continuous. MathsIsFuns example is about continuous routes, not smooth ones. You could e.g. walk up the side of a pyramid to the apex and down the another side in which case no part of your route is horizontal.
This is a very important result indeed. As Bertrand Russell and Alfred North Whitehead showed in their magnum opus Principia Mathematica, it is necessary to prove that 1 + 1 = 2 in order to re-invent mathematics with set theory.
[align=center]http://www.youtube.com/watch?v=BE657F9sqyQ[/align]
And
I also thrashed the computer at Othello! Look!
[align=center][/align]
HAHAHAHAHA!!!!
Ive just played Five In A Line and given the computer a jolly good thrashing! Not only did I get five in a line, I actually got a six in a line and an additional five in a line!
[align=center][/align]
HAHAHAHAHA!!!!
Thanks! Fixed.
The point is that if your number is an odd multiple of 5, step 3 will produce a number ending in 24, while if your original number is a multiple of 10, step 3 will produce a number ending in 99. I forgot about the latter.
This is the latest number game invented by yours truly.
(1) Think of an integer and square it.
(2) Multiply together the number before and the number after the resulting square.
(3) If the last digit of the new number is 4 or 9, add 3; if the last digit is not 4 or 9, add 2.
(4) Multiply by 20 and subtract 29.
Hence, if n is the number of 1s,
Now
Thus
Hence we have the required formula
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[/align]