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        riddles >> medium >> equation of doom
        
(Message started by: srn347 on Sep 11^th, 2007, 5:13pm)

Title: equation of doom
Post by srn347 on Sep 11^th, 2007, 5:13pm

x^y -y=x^5 -y^4 -y^3=20 x>0 y>0

Title: Re: <insert subject here>
Post by ThudanBlunder on Sep 11^th, 2007, 5:45pm

You haven't written a subject title and you haven't written a question.

No question, no answer, dig? Subject titles are necessary so that one can easily find puzzles again. For instance, sometimes members might want to cite examples of puzzles posted by people who haven't a clue, and if you give your threads titles they can easily remember yours.

In fact, all you have done is steal Jock's sig and started an untitled lthread with it!
Please stop polluting this forum with your cretinous behaviour.

Title: Re: <insert subject here>
Post by srn347 on Sep 11^th, 2007, 7:14pm

First of all, it is a question. I didn't steal the sig, I used it as a springboard(I stole the springboard). And this forum isn't polluted. Why is your ambition to destroy my mind(not that it's working)?!

Title: Re: equation of doom
Post by Grimbal on Sep 12^th, 2007, 2:54am

Pieces of pie. ;)

Title: Re: <insert subject here>
Post by ThudanBlunder on Sep 12^th, 2007, 3:11am

on 09/11/07 at 19:14:29, srn347 wrote:

First of all, it is a question.

An equation is not a question. It is a statement.
If you use somebody's else's sig you ought to attribute it to them, not disingenuously post it as a question without a question mark.

Title: Re: equation of doom
Post by srn347 on Sep 12^th, 2007, 8:16pm

An equation is a question, asking what x and y are. And since you mentioned whos sig it is, I guess attribution is out of the question until next time.

Title: Re: equation of doom
Post by mikedagr8 on Sep 12^th, 2007, 8:18pm

on 09/12/07 at 20:16:37, srn347 wrote:

An equation is a question, asking what x and y are. And since you mentioned whos sig it is, I guess attribution is out of the question until next time.

So in this equation "5*4=20" where are the x and y?

What you are after is instead of this

Quote:

x^y -y=x^5 -y^4 -y^3=20 x>0 y>0

is this "x^y -y=x^5 -y^4 -y^3=20 ; x>0 y>0 "

Title: Re: equation of doom
Post by srn347 on Sep 12^th, 2007, 8:39pm

5*4=20 is an identity, since x and/or y dropped out of the equation. They can be anything. Regardless, can any of you try the equation instead of obsessing over the fact that it is someones sig?

Title: Re: equation of doom
Post by Grimbal on Sep 13^th, 2007, 1:19am

Well, I gave up calculating an exact answer. The x^y part makes it probably impossible.

But numerically, I find an amusing result which I hinted at.
x and y are [hide] close to pi and e [/hide].

Title: Re: equation of doom
Post by srn347 on Sep 13^th, 2007, 4:44pm

Possibly. x^y isn't what makes it nearly impossible, x^5-y^4-y^3 is.

Title: Re: equation of doom
Post by Obob on Sep 13^th, 2007, 6:32pm

No, the x^y is much more difficult to deal with. In fact, x^5-y^4-y^3=20 allows you to eliminate one of the variables.

Title: Re: equation of doom
Post by ThudanBlunder on Sep 13^th, 2007, 6:48pm

on 09/12/07 at 20:16:37, srn347 wrote:

An equation is a question, asking what x and y are.

It is a question only in that we must try to figure out what x and y are allowed to be, eg. integers, reals, etc.

Title: Re: equation of doom
Post by srn347 on Sep 13^th, 2007, 9:22pm

They have to be more than zero(clearly). Other than that, try to keep it real(especially an integer), but if you find any other solution, try it anyway.

Title: Re: equation of doom
Post by towr on Sep 14^th, 2007, 5:47am

You can rework the equations to
x = (y^4 +y^3 +20)^(1/5)
y = log(y +20)/log(x)
and use these to iteratively approximate x and y

giving (in my case, using javascript and 100 iterations)
2.718300263323929 and 3.1416110348231654
As Grimbal said, pretty much e and pi respectively.

Title: Re: equation of doom
Post by srn347 on Sep 15^th, 2007, 3:51pm

I've tried it. It is about equal to 20 in that case, but not exactly.

Title: Re: equation of doom
Post by towr on Sep 16^th, 2007, 12:26pm

Well, that's why it's called an approximation.
I doubt there is a (simple) exact answer. (You could give an exact answer using e.g. limits, but that wouldn't be very informative)

Title: Re: equation of doom
Post by Sameer on Sep 16^th, 2007, 12:47pm

on 09/13/07 at 21:22:20, srn347 wrote:

They have to be more than zero(clearly). Other than that, try to keep it real(especially an integer), but if you find any other solution, try it anyway.

You got an integer solution? I would like to see that!!! ;) And no one liners: proper method and explanation!!

Title: Re: equation of doom
Post by ThudanBlunder on Sep 16^th, 2007, 1:55pm

on 09/16/07 at 12:47:06, Sameer wrote:

You got an integer solution? I

He ain't got zip! He just likes asking questions he doesn't understand.

Title: Re: equation of doom
Post by srn347 on Sep 16^th, 2007, 4:11pm

I have more than zip! Though the part about me not knowing the answer is correct. The next question I ask will have an answer I know of, if it has an answer...