1. $\left\{\begin{array}{l l} x^2-3xy+2y^2=0,\\ x^2+y^2=20 \end{array}\right.$
2. $\left\{\begin{array}{l l} x^2+y^2-3xy+4x+4y=-9,\\ xy-3x-3y=7\end{array}\right.$
3. $\left\{\begin{array}{l l} y^2+2xy=15,\\ 2x^2+xy=5 \end{array}\right.$
4. $\left\{\begin{array}{l l} x^2-2xy+y^2=9,\\ 4x^2+xy+4y^2=18\end{array}\right.$
5. $\left\{\begin{array}{l l} \displaystyle\frac{2}{2x-y}+\frac{3}{x-2y}=\frac{1}{2},\\ \displaystyle\frac{2}{2x-y}-\frac{1}{x-2y}=\frac{1}{18} \end{array}\right.$
6. Найдите $x+y+4z$, если $\left\{\begin{array}{l l} 2x+3y+2z=13,\\ 3x+5y=-7\end{array}\right.$.
7. $\left\{\begin{array}{l l} xy(x-y)=-20,\\ \displaystyle\frac{1}{x}-\frac{1}{y}=\frac{5}{4} \end{array}\right.$

Ответы

1. $(\sqrt{10};\sqrt{10}), (-\sqrt{10}; -\sqrt{10})$
2. (-1; -1)
3. (1; 3), (-1;-3)
4. (2;-1), (-1;2), (-2;1), (1;-2)
5. (5; -2)
6. 33
7. (1; -4), (4;-1), $(\frac{-5+\sqrt{41}}{2};\frac{5+\sqrt{41}}{2}), (\frac{-5-\sqrt{41}}{2};\frac{5-\sqrt{41}}{2})$