c/
\(\Leftrightarrow\left[{}\begin{matrix}x^2+x+1=0\\6-2x=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left(x+\frac{1}{2}\right)^2+\frac{3}{4}=0\left(vn\right)\\2x=6\end{matrix}\right.\) \(\Rightarrow x=3\)
d/
\(\Leftrightarrow\left[{}\begin{matrix}x^2+2x+2=0\\8x-4=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left(x+1\right)^2+1=0\\8x=4\end{matrix}\right.\) \(\Rightarrow x=\frac{1}{2}\)