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MathNet 2021 — Part 09 Question 25

Math Olympiad Vault · MathNet 2021 — Part 09

Question 25

We say that the triple $a, b, c$ from the segment $[-1; 1]$ is *worthy*, if these numbers satisfy the inequality $1 + 2abc \gt a^2 + b^2 + c^2$. Prove that if the triples $a, b, c$ and $x, y, z$ are worthy, then $ax, by, cz$ is worthy as well.

(Voloshyn Denys)