MathDB
Very similar to (actually same) KMO P3

Source: 2015 Korean Junior MO P4

November 1, 2015
algebrainequalities

Problem Statement

Reals a,b,c,x,ya,b,c,x,y satisfy a2+b2+c2=x2+y2=1a^2+b^2+c^2=x^2+y^2=1. Find the maximum value of (ax+by)2+(bx+cy)2(ax+by)^2+(bx+cy)^2