IMO Shortlist 1973 problem 2
Dodao/la:
arhiva2. travnja 2012. Given a circle
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, find the locus of vertices
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of parallelograms
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with diagonals

, such that

is inside

.
%V0
Given a circle $K$, find the locus of vertices $A$ of parallelograms $ABCD$ with diagonals $AC \leq BD$, such that $BD$ is inside $K$.
Izvor: Međunarodna matematička olimpijada, shortlist 1973