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MathNet 2025-part-02 — 186 problems (EN–VI) Question 154

Math Olympiad Vault · MathNet 2025-part-02 — 186 problems (EN–VI)

Question 154

Complex numbers $\omega_{1}$, $\ldots$, $\omega_{n}$ each have magnitude $1$. Let $z$ be a complex number distinct from $\omega_{1}$, $\ldots$, $\omega_{n}$ such that
$$
\frac{z + \omega_{1}}{z - \omega_{1}} + \dots + \frac{z + \omega_{n}}{z - \omega_{n}} = 0.
$$
Prove that $|z| = 1$.