Suppose that the point M lying in the
interior of the parallelogram ABCD,
two parallels to AB and AD are drawn,
intersecting the sides of ABCD at the
points P, Q, R, S (See Figure). Prove
that M lies on the diagonal AC if and
only if [MRDS] = [MPBQ].
Find the point in interior of a convex
quadrilateral such that the sum of its
distances to the 4 vertices is minimal.
Find the point in interior of a convex
quadrilateral such that the sum of its
distances to the 4 sides is minimal.