Does $ \frac{z}{x+y}+\frac{y}{x+z} +\frac{z}{x-y}+\frac{y}{x-z}=9$ have a nonzero integer solution?
问题内容
I came up with the following Diophantine equation:
$$ \frac{z}{x+y}+\frac{y}{x+z} +\frac{z}{x-y}+\frac{y}{x-z}=9, $$
where $x,y,z\in\mathbb Z,$ $xyz\ne0,$ and $x+y\ne0,$ $x-y\ne0,$ $x+z\ne0,$ $x-z\ne0.$
Does this equation have a nonzero integer solution?
If a solution exists, I would be interested in finding one, preferably a primitive solution satisfying $\gcd(x,y,z)=1$.
If no such solution exists, is there a proof of nonexistence?
I came up with this equation and became curious whether it has any nonzero integer solutions. I am particularly interested in whether the structure of the denominators (x\pm y) and (x\pm z) can be used to prove the existence or nonexistence of integer solutions.
I have not yet found a solution or a proof of nonexistence.
Any ideas or approaches would be appreciated.
回答 (1)
Solution idea: Writing $a=\frac{y}{x}$ and $b=\frac{z}{x}$ the equation is equivalent to $$ \frac{2a}{1-b^2}+\frac{2b}{1-a^2}=9. $$ This leads to an elliptic curve having no rational points so that the only rational solutions are $$ (a,b)=(0,9/2),(9/2,0), $$ which contradicts $xyz\neq 0$.