1996 OIM Problems/Problem 6

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Problem

There are $n$ different points $A_1, \cdots , A_n$ in the plane and each point $A_i$ has been assigned a real number $\lambda _i$ other than zero, so that

\[(\overline{A_iA_j})^2 = \lambda _i + \lambda _j\]

\[\text{for all } i, j \text{ with } i \ne j\text{.}\]

Show that

a) $n \le 4$

b) If $n=4$, then $\frac{1}{\lambda _1}+\frac{1}{\lambda _2}+\frac{1}{\lambda _3}+\frac{1}{\lambda _4}=0$

~translated into English by Tomas Diaz. ~orders@tomasdiaz.com

Solution

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See also

https://www.oma.org.ar/enunciados/ibe11.htm