Community

Looking for a challenging algebra text? Preparing for MATHCOUNTS or the AMC exams?
Check out Art of Problem Solving's Introduction to Algebra by Richard Rusczyk.
Login Register Memberlist Search AoPS Blogs Contests Galleries Forum Index
The time now is Sun Nov 22, 2009 7:38 pm
All times are UTC - 8
View posts since last visit
View unanswered posts
inequality
Moderators: High School Olympiad Moderators, Arne, blahblahblah, Cezar Lupu, darij grinberg, harazi, Megus, N.T.TUAN, orl, pbornsztein, pvthuan
Post new topic   Reply to topic View previous topicView next topic
4 Posts • Page 1 of 1
Author Message
Mahan73
New Member
New Member

Offline
Joined: 22 Aug 2009
Posts: 12
Iran, Islamic Republic of

To rate posts you must be logged in
#1
inequality

a,b,c,d\ are\ positive\ real\ numbers\ such\ that\ \ \sum{\frac {1}{a^4 + 1}} = 3\ \ \ \ \ prove\ that\ \sum{a^2b^2\le 2}
Last edited by Mahan73 on Sat Nov 07, 2009 7:55 am; edited 1 time in total 
PostPosted: Sat Nov 07, 2009 1:18 am  Back to top 
  ProfilePM
Mahan73
New Member
New Member

Offline
Joined: 22 Aug 2009
Posts: 12
Iran, Islamic Republic of

To rate posts you must be logged in
#2
any Reply?

It's Iran's second round problem with a little change................
why there isn't any reply? Blush

PostPosted: Sat Nov 07, 2009 7:55 am  Back to top 
  ProfilePM
dnkywin
Riemann Hypothesis
Riemann Hypothesis


Offline
Joined: 29 Jan 2008
Posts: 385
Location: Dude don't be a stalker... Location: Dude don't be a stalker... Location: Dude don't be a stalker...

To rate posts you must be logged in
#3
Click to reveal hidden content
Suppose \sum\limit_{sym}{a^{2}b^{2}> 2. By Muirhead, this would imply \sum\limit_{sym}a^4> 4/3. Now by C-S, \frac{16}{3}\left(\frac{1}{a^4+1}+\frac{1}{b^4+1}+\frac{1}{c^4+1}+\frac{1}{d^4+1}\right)<\left(a^4+b^4+c^4+d^4+4\right)\le.... Thus \sum\limit_{sym}{a^{2}b^{2}> 2\implies \frac{1}{a^4+1}+\frac{1}{b^4+1}+\frac{1}{c^4+1}+\frac{1}{d^4+1}<3, a contradiction.

_________________
dnkywin %is beast

Visit my blog!

PostPosted: Sat Nov 07, 2009 5:18 pm  Back to top 
  ProfilePMBlog
Abdek
P versus NP
P versus NP


Offline
Joined: 22 Aug 2009
Posts: 49
Location: Morocco
MoroccoEuropean Union

To rate posts you must be logged in
#4
Let a^4 = \frac {x}{y + z + t} and b^4 = \frac {y}{z + t + x} and etc..

The inequality may be written as :

\sum_{sym}\sqrt {\frac {xy}{(y + z + t)(z + t + x)}} \le 2

Using AM-GM inequality

\sum_{sym}\sqrt {\frac {xy}{(y + z + t)(z + t + x)}} \le \sum_{sym}\frac {1}{2}\left(\frac {y}{y + z + t} + \frac {x}{x + t +...
_________________
Mharchi Abdelmalek

PostPosted: Sun Nov 08, 2009 10:11 am  Back to top 
  ProfilePM
Display posts from previous:   Sort by:   
4 Posts • Page 1 of 1
Post new topic   Reply to topic View previous topicView next topic
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
You cannot post calendar events in this forum


© Copyright 2008 AoPS Incorporated. All Rights Reserved. • FoundationPrivacyContact Us