These questions are inspired by Yaglom and Boltyanskii's classic, 'Convex Figures'.
Y and B prove this theorem
Winternitz Theorem: If a convex figure is divided into 2 parts by a line l that passes through its
center of gravity, the ratio of the areas of the two parts always lies between between the bounds 4/5 and 5/4.
They also prove that for any triangle, there is no other point O than its center of gravity (centroid) for which the ratio of the partial areas
into which the triangle is subdivided by lines thru O can be enclosed within narrower bounds.
Question 1: For any general convex 2D region, is the centre of mass still the point such that the areas into which the region is divided
by lines thru that points are closest to each other? If the point we seek is not necessarily the
centre of mass, then it could be called the 'area partition center' of the region and finding this center for a general given region
could be an algorithmic question.
Y and Balso prove:
Let a bounded curve of length L that may consist of separate pieces be given in the plane. Then there is a point O in the plane
so that each line through O divides the curve into 2 parts each having a length of not less than L/3.
Question 2: If L be the boundary of a single convex region, there must be a point O' in its interior such that any line thru O' divides the
boundary into 2 portions such that the lengths of the two portions are closer than 1:3. What is a bound for this ratio for convex regions?
Let us define the perimeter partition center of a convex region as that point P in its interior such that
the 2 portions into which any line thru P divides the outer boundary are guaranteed to be closest to each other in length.
Example: For an isosceles triangle with very narrow base, this perimeter partition center is close to the mid point of the median
of its apex and so clearly different from the centroid.
Question 3 Given a general convex region (even a triangle) to find its perimeter partition center.
Note: These questions have 3D analogs with volume and surface area replacing area and perimeter.
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