I'm trying to find integer solutions to: $2x^2+25=y^3$.
Here's what I've managed to do so far:
- y is odd. y and x are co-prime.
- In $\mathbb{Q}(\sqrt{2},i)$ we can write: $(\sqrt{2}x+5i)(\sqrt{2}x-5i)=y^3$.
- Using (1) I showed $(\sqrt{2}x+5i)$ and $(\sqrt{2}x-5i)$ are co-prime.
- So assuming we have unique factorization (do we?) we have $a^3=\sqrt{2}x+5i$ and $b^3=\sqrt{2}x-5i$ for some $a,b$ in the ring of integers of $\mathbb{Q}(\sqrt{2},i)$.
- I also know that an integral base in $\mathbb{Q}(\sqrt{2},i)$ is $\{1,\sqrt{2},i,\frac{1}{2}\sqrt{2}(1+i)\}$.
I have tried to write $a$ in general form and get some restrictions on its coefficients but all I've reached is that $a\equiv -\sqrt{2}x+i(\text{mod } 3)$.
Any direction will be highly appreciated.