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MathNet 2017-part-03 — 176 problems (EN–VI) Question 111

Math Olympiad Vault · MathNet 2017-part-03 — 176 problems (EN–VI)

Question 111

Let $a$, $b$, $c$ and $d$ be positive real numbers with $a + b + c + d = 2$. Prove that
$$
\frac{(a+c)^2}{ad+bc} + \frac{(b+d)^2}{ac+bd} + 4 \ge 4 \left( \frac{a+b+1}{c+d+1} + \frac{c+d+1}{a+b+1} \right).
$$