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POW: Inequalities
Posted:
Sun Apr 01, 2007 1:12 am
by AuSmith
Use the Rearrangement Inequality to show that...
(1) For nonnegative a,b,c, [unparseable or potentially dangerous latex formula]
(2) For positive a,b,c, [unparseable or potentially dangerous latex formula]
(3) [unparseable or potentially dangerous latex formula]
(4) For all a,b,c, [unparseable or potentially dangerous latex formula]
From Engel Ch. 7.
Posted:
Sun Apr 01, 2007 9:07 am
by polymath25
I can do number 1, but I don't know how to use LaTeX and it'd be too complicated without it.
Posted:
Sun Apr 01, 2007 10:11 am
by AuSmith
Posted:
Sun Apr 01, 2007 12:29 pm
by polymath25
Sorry, misread #1, but i can do #2:
Assume that [unparseable or potentially dangerous latex formula] so that [unparseable or potentially dangerous latex formula] and [unparseable or potentially dangerous latex formula] are similarly arranged.
Thus [unparseable or potentially dangerous latex formula]
and
[unparseable or potentially dangerous latex formula]
Adding these together gives us:
[unparseable or potentially dangerous latex formula]
The second part of this inequality gives us 3 (proof to long to type out), and then upon dividing both sides by 2 you get
[unparseable or potentially dangerous latex formula]
Posted:
Sun Apr 01, 2007 2:52 pm
by AuSmith
it appears #1 was supposed to say nonnegative numbers. Say, [unparseable or potentially dangerous latex formula], then [unparseable or potentially dangerous latex formula], which is clearly untrue. Sorry, 'bout that. You should be able to do it now.
Posted:
Sun Apr 01, 2007 3:41 pm
by stupidityismygam
1) very trivial but what the heck
WLOG assume [unparseable or potentially dangerous latex formula] then [unparseable or potentially dangerous latex formula]
So then by rearrangement [unparseable or potentially dangerous latex formula] as desired
for 2) i did a combination of Cauchy and Rearrangment, if you want to see my solution tell me
Posted:
Sun Apr 01, 2007 4:30 pm
by AuSmith
Posted:
Sun Apr 01, 2007 4:51 pm
by polymath25
I'm assuming that if I got #3 without using Rearrangement Inequality, then it's cheating
Re: POW: Inequalities
Posted:
Sun Apr 01, 2007 4:59 pm
by stupidityismygam
Re: POW: Inequalities
Posted:
Sun Apr 01, 2007 5:50 pm
by AuSmith
Posted:
Sun Apr 01, 2007 9:02 pm
by makashi
#2 is Nesbitt's Inequality
I believe the standard approach is to add three to both sides:
[unparseable or potentially dangerous latex formula]
If the first factor, [unparseable or potentially dangerous latex formula] is rewritten as [unparseable or potentially dangerous latex formula], then either Cauchy-Schwartz or Rearrangement (Chebyshev, as [unparseable or potentially dangerous latex formula] and [unparseable or potentially dangerous latex formula] are oppositely sorted) will do the trick:
[unparseable or potentially dangerous latex formula]
#4. Although there is mention of some scalar Rearrangement form, if I remember correctly, Engel never proves it, so we'll resort to other methods first, such as the Trivial Inequality:
[unparseable or potentially dangerous latex formula]
[unparseable or potentially dangerous latex formula]
We can use the Rearrangement Inequality (or many others) to show that
[unparseable or potentially dangerous latex formula]
By transitivity, [unparseable or potentially dangerous latex formula] and the desired result follows.