\[\begin{array}{l}
\sqrt {4{{\rm{x}}^2} - 4{\rm{x}} + 1} = |4 - {x^2}|\\
\Leftrightarrow \sqrt {{{\left( {2{\rm{x}} - 1} \right)}^2}} = |4 - {x^2}|\\
\Leftrightarrow |2{\rm{x}} - 1| = |4 - {x^2}|\\
\Leftrightarrow \left[ \begin{array}{l}
2{\rm{x}} - 1 = 4 - {x^2}\\
2{\rm{x}} - 1 = {x^2} - 4
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
{x^2} + 2{\rm{x}} - 5 = 0\\
{x^2} - 2{\rm{x}} - 3 = 0
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
{x^2} + 2{\rm{x}} + 1 = 6\\
{x^2} - 2{\rm{x}} + 1 = 4
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
{\left( {x + 1} \right)^2} = 6\\
{\left( {x - 1} \right)^2} = 4
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x + 1 = \sqrt 6 \\
x + 1 = - \sqrt 6 \\
x - 1 = 2\\
x - 1 = - 2
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = \sqrt 6 - 1\\
x = - \sqrt 6 - 1\\
x = 3\\
x = - 1
\end{array} \right.\\
Vay:S = \{ \sqrt 6 - 1; - \sqrt 6 - 1;3; - 1\}
\end{array}\]

√(4x² - 4x + 1) = |4 - x²|

<=> (4x² - 4x + 1)=(4 - x²)2

<=> (4x² - 4x + 1)=16-8x²+x4

x=3,x=-1,x^2+2x-5=0

x=√6−1,x=−√6−1,x=3,x=−1