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How can I prove that the equation $x^2 \equiv -1 \pmod {p^k} $, where $p$ is an odd prime and $p \equiv 1 \pmod 4$ and $k$ is any integer, has exactly two solutions?

Thank you!

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closed as off-topic by Carl Mummert, YiFan, John Omielan, Leucippus, Cesareo Mar 2 at 0:51

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