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MathNet 2018-part-06 — 181 problems (EN–VI) Question 138

Math Olympiad Vault · MathNet 2018-part-06 — 181 problems (EN–VI)

Question 138

Let $[x_1, x_2]$ and $[y_1, y_2, y_3]$ be the least common multiple of $x_1, x_2$ and $y_1, y_2, y_3$ respectively. For any positive integers $a, b, c, d$ let $A$ and $B$ be such that:
$$
A = [a, b, c] \cdot [a, b, d] \cdot [a, c, d] \cdot [b, c, d] \text{ and } B = [a, b] \cdot [a, c] \cdot [a, d] \cdot [b, c] \cdot [b, d] \cdot [c, d].
$$

Show that $A^6 \geq B^4$.