Giai hệ phương trình:
1,\(\left\{{}\begin{matrix}\sqrt{x+1}+\sqrt{y}=4\\x+y=7\end{matrix}\right.\) 2,\(\left\{{}\begin{matrix}x^2+y^{^2}-xy=1\\x^3+y^3=x+3y\end{matrix}\right.\) 3,\(\left\{{}\begin{matrix}6x^2-3xy+x+y=1\\x^2+y^2=1\end{matrix}\right.\)