3.21 Expected values Suppose that two points (X1, Y1) and (X2, Y2) are uniformly and independently distributed over a circle of area A. Assume that the travel distance D between the two points is the right-angle travel distance

D = | X1 - X2| + |Y1 - Y2|

Argue that

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Hint: Consider D to be the product of the Euclidean distance and a scaling factor R, the ratio between the right-angle and Euclidean distances.