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## #1 2014-02-09 04:41:46

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

Hey guys.I have a little question or just a personal wonder about them.

Question is:
for any
?
?
Test:

Last edited by Yusuke00 (2014-02-09 04:57:39)

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## #2 2014-02-09 04:42:55

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Question about polynomial ecuation

Hi;

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #3 2014-02-09 04:52:09

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

### Re: Question about polynomial ecuation

Done yeah cool now i found out how it works. hehe

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## #4 2014-02-09 04:53:10

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Question about polynomial ecuation

Hi;

How can K be an element of R?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #5 2014-02-09 04:55:51

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

### Re: Question about polynomial ecuation

It's N* sorry math. I don't really know how to write N* or R*+.How you do that?

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## #6 2014-02-09 04:58:34

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Question about polynomial ecuation

You can just put N or R. You can use

http://www.codecogs.com/latex/eqneditor.php

for all ypur latexing.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #7 2014-02-09 09:46:33

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

### Re: Question about polynomial ecuation

Not any opinions/ideas yet?

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## #8 2014-02-09 18:01:22

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Question about polynomial ecuation

Yusuke00 wrote:

Hey guys.I have a little question or just a personal wonder about them.

Question is: Is
for any
?
?

Fixed the post a bit.

Why would you think they cannot be positive?

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #9 2014-02-10 02:35:06

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

### Re: Question about polynomial ecuation

You got it wrong.
In my opinion the first one is always positive for any x real but i don't really know how to prove it.

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## #10 2014-02-10 02:47:37

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Question about polynomial ecuation

Hi;

That is the gf for that sum. It is obviously positive when x >=0. You might now try to prove that the numerator and denominator have the same sign for x<0.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #11 2014-02-10 03:19:38

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

### Re: Question about polynomial ecuation

That would be quite hard.
I know the problem is to prove that x does not have roots on (-1,0) because it's easy to see on the other cases.Ideas?

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## #12 2014-02-10 03:35:40

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Question about polynomial ecuation

Hi;

Is it really that hard?

Take the numerator when x<0. It is obvious that x^(2k+1) is always negative and therefore x^(2k)-1 is always negative.

Now the denominator is obviously negative for x<0, so we have (-) / (-) which is always positive.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #13 2014-02-10 04:02:37

Yusuke00
Member
Registered: 2013-11-19
Posts: 43

### Re: Question about polynomial ecuation

Indeed,good point you are right.

http://www.mathsisfun.com/data/function-grapher.php?func1=sqrt%28x%29&func2=2

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## #14 2014-02-10 15:20:59

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Question about polynomial ecuation

Or, you could just say that, for any integer n, x^(2n)>0.

Also, I was confused by the question. It seems, by what you wanted, that it should have been "Is f>0 for every x in R?".

Last edited by anonimnystefy (2014-02-10 15:22:08)

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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