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MathNet 2015-part-03 — 191 problems (EN–VI) Question 42

Math Olympiad Vault · MathNet 2015-part-03 — 191 problems (EN–VI)

Question 42

Let $a_1, a_2, \dots, a_n$ be a sequence of real numbers lying between $1$ and $-1$, i.e. $-1 \lt a_i \lt 1$, for $1 \le i \le n$, and such that

(i) $a_1 + a_2 + \dots + a_n = 0$;

(ii) $a_1^2 + a_2^2 + \dots + a_n^2 = 40$.

Determine the smallest possible value of $n$.