255. Find the rational solutions of the equation $x^{2}$ $-3 y^{2}=1$.


255. $(x+1)(x-1)=3 y \cdot y, \frac{x+1}{y}=\frac{3 y}{x-1}=k$;

$$
x=\frac{k^{2}+3}{k^{2}-3}, y=\frac{2 k}{k^{2}-3}
$$

where $k$ is an arbitrary rational number.