247. Find a parallelogram with integer sides and diagonals.
247. Denoting the sides by $x$ and $y$, and the diagonals by $z$ and $u$, we get the equation:

$$
2\left(x^{2}+y^{2}\right)=z^{2}+u^{2}
$$

Answer. $\quad x=2 r^{2}-2 s^{2}+2 s t-t^{2}, \quad y=2 r t-4 r s, \quad z=$ $=2 r^{2}+2 s^{2}-4 s t+t^{2}, u=2 r^{2}+2 s^{2}-t^{2}$.

Example. $r=7, s=1, t=3$; then $x=93, y=14$, $z=97, u=91$.