How many integral solutions are there for the following equation?
This is a part of the set Polynomial Diophantine Equations
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Given : x 6 + 3 x 4 + 6 x 2 + 5 = y 3
Consider the L.H.S.
x 6 + 3 x 4 + 6 x 2 + 5
= x 6 + 3 x 4 + 3 x 2 + 1 + 3 x 2 + 3 + 1
= ( x 2 + 1 ) 3 + 3 ( x 2 + 1 ) + 1
Let t = x 2 + 1 ; t > 0
⟹ t 3 + 3 t + 1 = y 3
Note that t 3 < t 3 + 3 t + 1 < ( t + 1 ) 3
But an integral cube cannot exist in between two consecutive integral cubes.
⟹ Number of solutions = 0