giải HPT
$1.$ $\left\{\begin{matrix} x+y+\sqrt{2y-1}+\sqrt{x-y}=5 & \\ y^2+2=xy+y & \end{matrix}\right.$
$2$.$\left\{\begin{matrix} 2x^2+\sqrt{2x}=(x+y)y+\sqrt{xy} \\ \sqrt{x-1}+xy=\sqrt{y^2+21} \end{matrix}\right.$
$3$.$\left\{\begin{matrix}x-y\sqrt{2-x}+2y^2=2 \\ 2(\sqrt{x+2}-4y)+8\sqrt{y}.\sqrt{xy+2y}=34-15x \end{matrix}\right.$
$4$ $\left\{\begin{matrix}x+y+\sqrt{x^2-y^2}=12 \\ y\sqrt{x^2-y^2}=12 \end{matrix}\right.$.
