Re: IMO LL Inequality problem
Jensen's is well-known to all competitors these days, and, as I said, my application of it is not particularly deep since Cauchy Schwarz gives us
\sum_i a_i^2/(a_i(S-a_i)) \geq S^2/(\sum_{i\not=j} a_ia_j)
which is exactly the same as what my application of Jensen's yields. My solution, at least with Cauchy Schwarz in place of Jensen's, is shorter, more rigorous, and almost certainly 'isomorphic' to the official solution.
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