280. One pair of roots of the system

$$
\begin{gathered}
2 x^{2}+3 x y+y^{2}=70 \\
6 x^{2}+x y-y^{2}=50
\end{gathered}
$$

is $x_{1}=3, y_{1}=4$; write another pair.
280. $x_{2}=-3, y_{2}=-4$. The left sides of the equations are even functions of both unknowns, i.e., expressions that do not change their values when $x$ is replaced by $-x$ and $y$ by $-y$.