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Question Number 198903 by necx122 last updated on 25/Oct/23

Find the minimum value of   (a/(b+c))+(b/(c+a))+(c/(a+b)) for all positive real  numbers

Findtheminimumvalueofab+c+bc+a+ca+bforallpositiverealnumbers

Commented by necx122 last updated on 25/Oct/23

please I need help with this

Answered by deleteduser1 last updated on 25/Oct/23

=(a^2 /(ab+ac))+(b^2 /(bc+ab))+(c^2 /(ac+bc))  ≥(((a+b+c)^2 =a^2 +b^2 +c^2 +2(ab+bc+ca))/(2(ab+bc+ca)))≥((3(ab+bc+ca))/(2(ab+bc+ca)))  =(3/2)[Equality when a=b=c]

=a2ab+ac+b2bc+ab+c2ac+bc(a+b+c)2=a2+b2+c2+2(ab+bc+ca)2(ab+bc+ca)3(ab+bc+ca)2(ab+bc+ca)=32[Equalitywhena=b=c]

Commented by necx122 last updated on 25/Oct/23

wow!!! This is a great solution sir. Please, I'm quite new to this manner of questions. Sir AST, can you please suggested sources where I can learn this properly. Thank you.

Commented by deleteduser1 last updated on 25/Oct/23

This is just an application of Cauchy−Schwarz  (Engel′s Form).

ThisisjustanapplicationofCauchySchwarz(EngelsForm).

Commented by necx122 last updated on 25/Oct/23

wow! This sounds like a sort of advanced level maths but how come I'm seeing such a question in junior mathematics olympiad? Could it mean that students in the junior school are really expected to know this? It's indeed overwhelming.

Commented by deleteduser1 last updated on 25/Oct/23

Not really advanced,they are standard techniques  in “olympiad” competitions.

Notreallyadvanced,theyarestandardtechniquesinolympiadcompetitions.

Commented by necx122 last updated on 25/Oct/23

hmmm... This is indeed a lot. Thank you for this information sir. I'm grateful.

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