Let ABCDEF be a convex hexagon. Let A', B', C', D', E', F' be the centroids of triangles FAB, ABC, BCD, CDE, DEF, EFA, respectively. (a) Show that every pair of opposite sides in hexagon A'B'C'D'E'F' (namely A'B' and D'E', B'C' and E'F', and C'D' and F'A') are parallel and equal in length. (b) Show that triangles A'C'E' and B'D'F' have equal areas.
Hi Gwen,
I have spent time playing with this question.
Graphically I have convinced myself that it is true.
I tried to follow Gavin's logic in the other answer but he seemed to jump a big step. Maybe what he was saying would have been more obvious if his pic had still been visible, but I doubt it.
However I did simply the problem to look only at one half of hexagon, which is a quadrilateral. The properties of each quadrilateral will be the same so if you can prove
1) B'C' is parallel to AD and that (that is what it always appears to be from my diagram.)
2) B'C' = one third of AD (also what it always appears to be from my diagram.)
then, by extension, you can prove what you are being asked.
Here is the interactive diagram that you can play with.
Only point A is fixed, the rest of the diagram can be dragged wherever you want. The stated requirements will stay correct.
https://www.geogebra.org/classic/hpyqwy5r