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MathNet 2017-part-07 — 172 problems (EN–VI) Question 149

Math Olympiad Vault · MathNet 2017-part-07 — 172 problems (EN–VI)

Question 149

Find the number of quadruples $(a, b, c, d)$ of integers with absolute value at most $5$ such that
$$
\left(a^{2}+b^{2}+c^{2}+d^{2}\right)^{2}=(a+b+c+d)(a-b+c-d)\left((a-c)^{2}+(b-d)^{2}\right)
$$