Number theoryDifficulty 5.2AIME, harderFind the answer
Solve the equation a3+b3+c3=2001 in positive integers.
Mircea Becheanu, Romania
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
To solve the equation a3+b3+c3=2001 in positive integers (a,b,c), we can explore possible values for a, b, and c that satisfy this equation.
First, calculate some bounds for the integers. Assume a≤b≤c, which implies 3a3≤2001. Thus, we find: a3≤32001≈667⇒a≤3667≈8.7. Since a must be an integer, we have a≤8.
Next, try possible values for a and find corresponding pairs (b,c) such that the sum of cubes equals 2001.
### Case a=1: b3+c3=2000 Explore values of b: 1. b=10, then c3=2000−103=2000−1000=1000⇒c=10.
Hence, one solution is (a,b,c)=(1,10,10).
### Case a=10: b3+c3=2001−103=2001−1000=1001 Explore values of b: 1. b=10, then c3=1001−103=1001−1000=1⇒c=1.
Thus, another solution is (a,b,c)=(10,10,1).
### Symmetric Cases: The nature of the problem allows permutation of a, b, and c, so we get additional solutions by permuting these variables: - (a,b,c)=(10,1,10).
Therefore, the solutions in positive integers are: (a,b,c)=(10,10,1),(10,1,10),(1,10,10)
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