Giải HPT:
1. $\left\{\begin{matrix} {x^2} + {y^2} + x - y = 4\\ x\left( {x - y + 1} \right) + y\left( {y - 1} \right) = 2 \end{matrix}\right.$
2. $\left\{\begin{matrix} \sqrt {x + y} + \sqrt {x - y} = 2\sqrt y \\ \sqrt x + \sqrt {5y} = 3 \end{matrix}\right.$
3. $\left\{\begin{matrix} {x^2}{y^2} + {y^4} + 1 = 3{y^2}\\ x{y^2} + x = 2y \end{matrix}\right.$
4. $\left\{\begin{matrix} x - y - \frac{{2y}}{x} = - 2\\ 2xy - 2{y^2} + x = 0\\ \end{matrix}\right.$
5. $\left\{\begin{matrix} x - 2y - \sqrt {xy} = 0\\ \sqrt {x - 1} - \sqrt {2y - 1} = 1 \end{matrix}\right.$