his position anywhere on earth. X, in possession of a GPS receiver, measures his distance from each of three satellites above, revealing that his distance from each creates a series of intersecting radii; each radius originates around a satellite and corresponds with the distance from X that satellite has been measured to be. 6
X's distance from A will indicate many points on earth that are along A's radius. However, factor X's distance from B into the equation, and the possible locations of X diminish, as he can now only be at a point somewhere along the radius of both A and B, that is, at those points where A and B intersect. A third reading from C will reveal X's actual location. In reality, readings from three satellites will narrow X's position to two possible points, not one. It should be noted, however, that one of these two points will be highly improbable given its distance from Earth or its projected velocity. This point of intersect is therefore discarded.7
The simple geometric principles discussed above r
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