LFD Book Forum Question 20
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#1
09-09-2012, 04:01 PM
 victe Junior Member Join Date: Aug 2012 Posts: 5
Question 20

I think there is two possible true answers to this question.
#2
09-09-2012, 08:43 PM
 yaser Caltech Join Date: Aug 2009 Location: Pasadena, California, USA Posts: 1,475
Re: Question 11

Quote:
 Originally Posted by victe I think there is two possible true answers to this question.
Could you pmail me why you think so?
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Where everyone thinks alike, no one thinks very much
#3
09-10-2012, 08:32 AM
 the cyclist Member Join Date: Jul 2012 Posts: 26
Re: Question 11

Quote:
 Originally Posted by victe I think there is two possible true answers to this question.
Hm. I don't think so. I can say the following without giving away too much info:

Out of the first four statements, I am sure three of them are false, because I can create simple counterexamples for them. For the remaining statement, I am not sure yet. (I am neither sure it is true, nor do I have a counterexample.)

So, I have narrowed it down to that one statement or "none of the above". Regardless, I am very confident that there are not two true statements in the list.
#4
09-10-2012, 08:38 AM
 TonySuarez Member Join Date: Jul 2012 Location: Lisboa, Portugal Posts: 35
Re: Question 11

Couldn't resist (but in the end perhaps I'll have to swallow...)
#5
09-10-2012, 08:47 AM
 feallertmalty Junior Member Join Date: Sep 2012 Posts: 1
Re: Question 11

Quote:
 Couldn't resist (but in the end perhaps I'll have to swallow...)
You narrated . On no other word
#6
09-12-2012, 05:20 AM
 victe Junior Member Join Date: Aug 2012 Posts: 5
Re: Question 11

Quote:
 Originally Posted by TonySuarez Couldn't resist (but in the end perhaps I'll have to swallow...)
In the end I was wrong.
I derived mathematically the true solution, and there is only one correct answer. Only, the statement should indicate some property on the functions to be met, but with the roles that are often used is understood.
Indeed, there are very simple counterexamples for all incorrect answers.
#7
09-14-2012, 10:05 AM
 TonySuarez Member Join Date: Jul 2012 Location: Lisboa, Portugal Posts: 35
Re: Question 11

Quote:
 Originally Posted by TonySuarez Couldn't resist (but in the end perhaps I'll have to swallow...)
I just jumped in, and delivered the final.
Worst than I expected :-(, lowered my percentile somewhat... but that's life...

So, in the end I had to swallow Q11, FYI :-(
#8
09-14-2012, 07:25 PM
 fgpancorbo Senior Member Join Date: Jul 2012 Posts: 104
Re: Question 11

Quote:
 Originally Posted by the cyclist Hm. I don't think so. I can say the following without giving away too much info: Out of the first four statements, I am sure three of them are false, because I can create simple counterexamples for them. For the remaining statement, I am not sure yet. (I am neither sure it is true, nor do I have a counterexample.) So, I have narrowed it down to that one statement or "none of the above". Regardless, I am very confident that there are not two true statements in the list.
I find myself in a similar situation! I spent a couple of hours trying to come up with the counter example to no avail. I then went analytical and I see no easy way to prove it. Still 4 days, so there is time for inspiration .
#9
09-14-2012, 08:42 PM
 yaser Caltech Join Date: Aug 2009 Location: Pasadena, California, USA Posts: 1,475
Re: Question 11

Quote:
 Originally Posted by fgpancorbo I find myself in a similar situation! I spent a couple of hours trying to come up with the counter example to no avail. I then went analytical and I see no easy way to prove it. Still 4 days, so there is time for inspiration .
Hint (from Mr. Hints himself ): Cauchy.

I hope this helps more than it confuses.
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Where everyone thinks alike, no one thinks very much
#10
09-14-2012, 09:01 PM
 fgpancorbo Senior Member Join Date: Jul 2012 Posts: 104
Re: Question 11

Quote:
 Originally Posted by yaser Hint (from Mr. Hints himself ): Cauchy. I hope this helps more than it confuses.
, sure, Cauchy like in "Cauchy-Schwarz"? I don't want to sound cocky but I thought about bringing that ammunition myself except that I was unable to identify the inner product but now that I think about it... there is that cross term that looks very much like one... Interesting. Correction; I said earlier that I had the proof, but I still have to work out the details on paper. I just did it in my mind; the actual details are a bit more elaborated but I don't see a problem getting there .

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