Karagota

<math>\left\{ \begin{matrix} xy\left - x \left-y\left=0\left; \\ \sqrt {\frac{{6x}}{{x+y}}} +\sqrt {\frac{{x+y}}{{6x}}}= {\frac{{5}}{{2}}} \\ \end{matrix} \right.

<math>\left\{ \begin{arraymatrix}{l} x^2 - x + a\le 0, \\ x^2 + 2x - 6a\le 0 \\ \end{arraymatrix} \right </math>