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MathNet 2026 — Part 05 Question 176

Math Olympiad Vault · MathNet 2026 — Part 05

Question 176

Suppose $x$, $y$, $z$ are positive numbers that sum to $\pi$. Prove that
$$
\frac{\sin 2x + \sin 2y + \sin 2z}{\sin x + \sin y + \sin z} \le 1,
$$
with equality iff $x = y = z = \pi/3$.