a, $\left\{ \begin{array}{l} 4x-y+3\sqrt{1+y}=0\\ 4\sqrt{(1+x)(1+y)}-6\sqrt{1+x} +1=0\end{array} \right.$b$\left\{ \begin{array}{l} x+y -1+\frac{1}{\sqrt{2x+y}}=0\\\frac{1}{x+y+1}+2\sqrt{2x+y} =2 \end{array} \right.$c$ \sqrt{2x^{2}+3x+1}+\sqrt{1-3x}=2\sqrt{x^{2}+1}$