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Given a rhombus, construct with straightedge and compass the foci of the ellipse tangent to its four sides at their midpoints.
Note: An ellipse is the locus of all points in a plane such that the sum of the distances to two fixed points, called the foci, is constant.
Note: An ellipse is the locus of all points in a plane such that the sum of the distances to two fixed points, called the foci, is constant.