Решите пожалуйста системы:

[tex]\left \{ {{x^{2}-xy=6 } \atop {y^{2}-xy=3 }} \right.[/tex]

[tex]\left \{ {{x^{2}-3xy+y^{2}=-1} \atop {2x^{2}+5xy-y^{2}=17}} \right.[/tex]

[tex]\left \{ {{\frac{3}{2x+y}+\frac{1}{2x-y}=\frac{2}{5}} \atop {\frac{7}{2x+y}+\frac{2}{2x-y}=\frac{3}{5}}} \right.[/tex]