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Roots- tricky Inequality question

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(edited 9 years ago)
I have no idea what question you are asking - can you express it symbolically?
Original post by atsruser
I have no idea what question you are asking - can you express it symbolically?

I asked Tenofthem.
However somebody could still help a lot.
Reply 3
Original post by MathMeister
I asked Tenofthem.
However somebody could still help a lot.


It's going to be difficult for someone else to help you unless you're more precise about what question you're asking - what's you've written so far is far too vague!
can you please write out the question as it was written? i have no idea what you're talking about

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(edited 9 years ago)
Original post by MathMeister
Ok... Let a,b,c be real numbers such that a^2+b^2+c^2=12. Find the maximum value of
a(8a)(a^2+4)+b(8b)(b^2+4)+c(8c)(c^2+4)


Currant Proofathon question (Q 5)
This is going against the honour code btw.
I used autograph and found the answer was however do not know how to prove the answer is the maximum value it can be mathematically.


what level is this?

i was thinking lagrange multipliers to maximise your function subject to the constraint a^2+b^2+c^2=12, but there's probably a more elegant method involving subbing the first function into the second one or something similar

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(edited 9 years ago)
Original post by Arithmeticae
what level is this?

i was thinking lagrange multipliers to maximise your function subject to the constraint a^2+b^2+c^2=12, but there's probably a more elegant method involving some work with the symmetry of the function

Posted from TSR Mobile

There is a very elegant method called autograph and other 3D graph plotters which show the answer in a picture. However, if you want to go against logic (and intrinsically what mathematicians like to do ( work things easily) then it's a higher level- I would guess.
Your way looks better. -
(edited 9 years ago)
Reply 8
Original post by MathMeister
There is a very elegant method called autograph and other 3D graph plotters which show the answer in a picture. However, if you want to go against logic (and intrinsically what mathematicians like to do ( work things easily) then it's a higher level- I would guess.
Your way looks better. - However could my idea still prove no higher number than 288 intersects the other graph (the constraint) .


I wouldn't call it a "method" - it's a piece of software that finds the answer for you!

I haven't studied competition maths, but I suspect what you're asking is the sort of thing that people who've done things like BMO and IMO could knock off fairly quickly - there's probably a smart inequality theorem you could use that will give you the answer :smile:
Original post by MathMeister
Ok... Let a,b,c be real numbers such that a^2+b^2+c^2=12. Find the maximum value of
a(8a)(a^2+4)+b(8b)(b^2+4)+c(8c)(c^2+4)




This certainly looks BMO-ish, so way out of my league, but I note that both expressions are symmetric under permutation of the variables, so I'm wondering if you can come up with a nice argument that we must have a=b=c for an extremum.
Original post by atsruser
This certainly looks BMO-ish, so way out of my league, but I note that both expressions are symmetric under permutation of the variables, so I'm wondering if you can come up with a nice argument that we must have a=b=c for an extremum.

I haven't technically even started AS level yet, so I do not understand the bold. However, yes, a,b,c all equal 2 and the Value (Max) = 288.
Original post by arkanm
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If you don't already, you should do Proofathon.
Original post by arkanm
Hey, I told you about that :tongue: (although I never actually do it)
Is it from proofathon?

Oh yes, so you did. Yes it is from proofathon. Technically this is a break of the honour code.
Original post by arkanm
Found it! : http://www.proofathon.org/Pages/ongoing_contest.php Hm, an on-going contest. Not to worry though; they're from AoPS, they'll never find us here! :tongue: (And you can submit my solution if you want, just saying.)

I already did :tongue:

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