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**Thanh Vân****Member**- Registered: 2011-07-17
- Posts: 10

Let a,b,c,d be positive real numbes. prove that

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**gAr****Member**- Registered: 2011-01-09
- Posts: 3,479

Hi Thanh Vân,

Welcome to the forum!

*Last edited by gAr (2011-07-17 04:19:09)*

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense" - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

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**Thanh Vân****Member**- Registered: 2011-07-17
- Posts: 10

Oh. Hi gAr. I don't understand your proof.

Why you have

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**gAr****Member**- Registered: 2011-01-09
- Posts: 3,479

Hi,

I thought since 8 is the minimum value LHS can have, we may write like that.

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense" - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 102,394

Hi;

For anyone else wishing to work on the problem here it is latexed.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **A number by itself is useful, but it is far more useful to know how accurate or certain that number is.**

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**Thanh Vân****Member**- Registered: 2011-07-17
- Posts: 10

I thinks idea of gAr is wrong and can't use it to prove inequality. It can solve by Cauchy Schwarz Inequality and AM-GM Inequality very beautiful.

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**gAr****Member**- Registered: 2011-01-09
- Posts: 3,479

Hi Thanh Vân,

Yes, I was wrong. I made wrong assumption without checking.

Anyway, I could prove

and

But unable to get anywhere.

*Last edited by gAr (2011-07-21 17:02:17)*

"Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense" - Buddha?

"Data! Data! Data!" he cried impatiently. "I can't make bricks without clay."

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