OK, quick: What spot on the earth is the farthest away from the center of the earth? Before you say "the top of Mount Everest," consider this: The earth is not a perfect sphere.
To figure out the right answer, you must approximate earth's diameter as an ellipsoid. You must also know the earth's polar diameter and its equatorial diameter. Then you can get down to business.
The process has been worked out in a blog post by John D. Cook, a research statistician at M. D. Anderson Cancer Center and associate faculty for the UT Graduate School of Biomedical Sciences. If you are interested in investing a few minutes to find out the answer, read his post: