AT-OEMO-FED1 2015 Problem 1

Let $a$ , $b$ , $c$ , $d$ be positive numbers. Prove that $(a^2 + b^2 + c^2 + d^2)^2 \ge (a+b)(b+c)(c+d)(d+a)$ When does equality hold?

(Georg Anegg)

Dataset text AI-MO AoPS. Quoted with source.

Solutions

No solution is on olymmath yet. Official and human solutions come first when they arrive. AI solutions come after them, with a label.