a.
\(\Leftrightarrow\dfrac{x-\sqrt{1+x^2}+x+\sqrt{1+x^2}}{\left(x-\sqrt{1+x^2}\right)\left(x+\sqrt{1+x^2}\right)}+2=0\)
\(\Leftrightarrow\dfrac{2x}{x^2-1-x^2}+2=0\)
\(\Leftrightarrow-2x+2=0\)
\(\Leftrightarrow x=1\)
b.
ĐKXĐ: \(x\ge a\)
Đặt \(\sqrt{x-a}=t\ge0\Rightarrow x=t^2+a\)
Pt trở thành:
\(2\left(t^2+a\right)-5at+2a^2-2a=0\)
\(\Leftrightarrow2t^2-5at+2a^2=0\)
\(\Leftrightarrow\left(2t-a\right)\left(t-2a\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}t=\dfrac{a}{2}\\t=2a\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x-a}=\dfrac{a}{2}\\\sqrt{x-a}=2a\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{a^2}{4}+a\\x=4a^2+a\end{matrix}\right.\)
