27/ $\left\{\begin{matrix} x+\sqrt{x(x^2-3x+3)}=\sqrt[3]{y+2}+\sqrt{y+3}+1 & \\ 3\sqrt{x-1}-\sqrt{x^2-6x+6}=\sqrt[3]{y+2}+1 & \end{matrix}\right.$
28/ $\left\{\begin{matrix} x^3-y^3-6y^2+3(x-5y)=14 & \\ \sqrt{3-x}+\sqrt{y+4}=x^3+y^2-5 & \end{matrix}\right.$
29/ $\left\{\begin{matrix} (1-y)\sqrt{x-y}+x=2+(x-y-1)\sqrt{y} & \\ 2y^2+4y+5x+1=(x-y+6)\sqrt{y(x^2+y+2)} & \end{matrix}\right.$
30/ $\left\{\begin{matrix} (1-y)\sqrt{x+y}+x+2y=2(x+y-1)\sqrt{y} & \\ y^2+2x+\sqrt[3]{y^4-2y^2}=4 & \end{matrix}\right.$
