Câu hỏi 103
Cho thấy rằng nếu $-1 \lt x \lt 1$, $-1 \lt y \lt 1$, $$
\left|\frac{x-y}{1-x y}\right| \leq \frac{|x|+|y|}{1+|x y|}
$$
\left|\frac{x-y}{1-x y}\right| \leq \frac{|x|+|y|}{1+|x y|}
$$
MathNet 2026 — Phần 03 Câu hỏi 103
Math Olympiad Vault · MathNet 2026 — Phần 03