Number theoryDifficulty 5.7AIME, harderProve itPhilippines
Problem: How many ordered pairs (x,y) of positive integers, where x<y, satisfy the equation x1+y1=20071
Solution
Solution: We can rewrite the given equation into (x−2007)(y−2007)=20072=34⋅2232 Since x<y, we have x−2007<y−2007. It follows that −2007<x−2007<2007or∣x−2007∣<2007 Thus, we have ∣y−2007∣>2007. x−2007133233342233⋅223y−200734⋅223233⋅223232⋅22323⋅2232223234⋅22333⋅223 For every pair of values of x−2007 and y−2007 in the above table, there is a corresponding pair of x and y. Thus, there are seven such ordered pairs.
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