解說

The question was: The shortest way to walk from place A to B is to go south for two miles, and then to the north for two miles. How far do you have to walk from place A to B by going east ?

It should be 6.28 miles.

Please see the following figure:

















Note that the first sentence of the question could only be true if S at the mid-point of a straight line joining A and B, and the definition of "east" is a circle that centers around the South (or North) pole. In fact, after walking for two miles and arrive at the South pole, any direction that you go further would be to the north. Nonetheless, the shortest way to go from A to B is by passing through S, A-S-B is therefore a straight line (in other words, theta equals 180-degree).