\(a;gọi\) \(x_o\) \(là\) \(ngo\) \(chung\Rightarrow\left\{{}\begin{matrix}x_o^2+x_o+a=0\\x_o^2+a.x_o+1=0\end{matrix}\right.\)
\(đk:\left\{{}\begin{matrix}\Delta1\ge0\\\Delta2\ge0\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}1-4a\ge0\\a^2-4\ge0\end{matrix}\right.\)\(\Leftrightarrow a\le-2\)
\(\Leftrightarrow x_o+a-ax_o-1=0\Leftrightarrow x_o=1\Rightarrow a=-2\left(tm\right)\)
\(b,TH1:vô\) \(nghiệm\Leftrightarrow\left\{{}\begin{matrix}\Delta1< 0\\\Delta2< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}1-4a< 0\\a^2-4< 0\end{matrix}\right.\)\(\Leftrightarrow\dfrac{1}{4}< a< 2\)
\(ycđb\Leftrightarrow\left\{{}\begin{matrix}x1+x2=x1'+x2'\\x1.x2=x1'.x2'\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}-1=-a\\a=1\end{matrix}\right.\)\(\Leftrightarrow a=1\left(tm\right)\)
