Saturday, February 2, 2019

number theory - Find all nonnegative integer solutions to $x^3 + 8x^2 − 6x + 8 = y^3$.




Find all nonnegative integer solutions to $x^3 + 8x^2 − 6x + 8 = y^3$.





The only solution I have found is $x=0$.



I have tried proving it by congruences and have had no success. I don't know how to prove it. I have even tried algebraic manipulation and have got



$$x(x^2 + 8x-6) = (y-2)(y^2 + 2y+4)$$



Could you please give me some ideas on how to proceed?


Answer



Hint:




Show that for $x$ large enough:
$$(x+2)^3Then you are left with very few cases to check.


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