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Take Quadratic And Cubic, Get Sum And Product (Posted on 2007-08-24) |
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Determine all possible positive integer triplets (x, y, z)
with y ≥ z satisfying the following system of equations :
x2 = 2(x+y+z)
x3- y3 - z3 = 3xyz
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Submitted by K Sengupta
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Rating: 3.8000 (5 votes)
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Solution:
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(Hide)
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From the second equation, we observe that x> y, z.
Accordingly, from the first equation, we obtain x^2 < 6x, so that :
x< 6.
The RHS of the first equation is even, so that x = 2, 4.
Suppose x=2. If so, we must have y+z = 0 in terms of the first
equation.. This does not admit of any positive integral solution
which is a contradiction.
Suppose x =4. Then the first equation yields y+z = 4. Imposing the
restriction y>=z, this has the solutions
(y, z) = (3, 1); (2, 2)
Thus, (x, y, z) = (4, 3, 1); (4,2, 2) correspond to all possible
solution to the given problem.
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Praneeth provides a solution to the general case of determining all possible integer triplets that satisfy conditions of the problem in this location.
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