IZhO 2005 Problem 4

For the positive real numbers $a,b,c$ prove that $\frac c{a + 2b} + \frac d{b + 2c} + \frac a{c + 2d} + \frac b{d + 2a} \geq \frac 43.$

Dataset text AI-MO AoPS. Quoted with source.

Solutions

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