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IMO 2010 — Complete Shortlist Question 25

IMO Shortlist · IMO 2010 — Complete Shortlist

Question 25

Find the smallest number $n$ such that there exist polynomials $f_{1}, f_{2}, \ldots, f_{n}$ with rational coefficients satisfying

$$
x^{2}+7=f_{1}(x)^{2}+f_{2}(x)^{2}+\cdots+f_{n}(x)^{2} .
$$