\(3+\left|x^2+1\right|=5\\ \Leftrightarrow\left|x^2+1\right|=5-3=2\\ \Leftrightarrow\left[{}\begin{matrix}x^2+1=2\\x^2+1=-2\left(vô.lí\right)\end{matrix}\right.\\ \Leftrightarrow x^2=1=1^2=\left(-1\right)^2\\ \Leftrightarrow x=\pm1\\ Vậy:S=\left\{\pm1\right\}\)
\(3+\left|x^2+1\right|=5\)
\(\Leftrightarrow\left|x^2+1\right|=2\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2+1=2\\x^2+1=-2\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2=1\\x^2=-1\left(loai\right)\end{matrix}\right.\)
\(\Leftrightarrow x=\pm\sqrt{1}\)
\(3+\left|x^2+1\right|=5\)
\(\Leftrightarrow\left|x^2+1\right|=2\)
\(\Rightarrow x^2+1=\pm2\)
\(\Rightarrow\left[{}\begin{matrix}x^2+1=2\\x^2+1=-2\left(vli\right)\end{matrix}\right.\)
\(\Leftrightarrow x=\pm1\)
