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A circular area of 5 miles radius covers 50265.5 acres (to 1 dp) Area = pi*radius2, which with radius in miles will give you area as 78.53982 square miles, then multiply by 64 â¦ 0, since there are 640 acres in 1 square mile.
By the way, the constant value 20,890,584 is the earthâs average radius in miles (3,956.55) multiplied by 5,280 feet per mile. The wikipedia article on haversine states that the average radius of the earth is 6,367.45 Km and Iâm assuming itâs correct.