July 27th, 2016, 08:09 AM  #1 
Newbie Joined: Jul 2016 From: Brazil Posts: 1 Thanks: 0  HMMT really hard problem
Find the largest real number y such that a² + b² + c² + d² ≥ ab + ybc + cd for all real numbers a, b, c and d. I tried to use the AMGM Inequality and I found 2 as the answer, but it's wrong! :/ 

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hard, hmmt, problem 
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