cau1:$\left\{ \begin{array}{l} x^{2}+y^{2}+\frac{8xy}{x+y}=16\\ \sqrt{x+y}=x^{2}-y\end{array} \right.$
cau2:$\left\{ \begin{array}{l} \sqrt{xy+(x-y)(\sqrt{xy}-2)}+\sqrt{x}=y+\sqrt{y}\\ (x+1)(y+\sqrt{xy}+x-x^{2})=4 \end{array} \right.$
cau3:$\left\{ \begin{array}{l} 5x^{2}y -4xy^{2}+3y^{3}-2(x+y)=0\\ xy(x^{2}+y^{2})+2=(x+y)^{2} \end{array} \right.$