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USAMO 2015 — Days 1 and 2 Question 5

USAMO · USAMO 2015 — Days 1 and 2

Question 5

Let $a$, $b$, $c$, $d$, $e$ be distinct positive integers such that $a^4+b^4=c^4+d^4=e^5$. Show that $ac+bd$ is a composite number.

Proposed by Mohsen Jamaali (credited by Evan Chen).