Đáp án:
7) \(\left[ \begin{array}{l}
x = 4\\
x = 1\\
x = 3\\
x = 2
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
5)\left| {{x^2} + 5x + 2} \right| = x + 7\\
\to \left[ \begin{array}{l}
{x^2} + 5x + 2 = x + 7\\
{x^2} + 5x + 2 = - x - 7
\end{array} \right.\\
\to \left[ \begin{array}{l}
{x^2} + 4x - 3 = 0\\
{x^2} + 6x + 9 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = - 2 + \sqrt 7 \\
x = - 2 - \sqrt 7 \\
x = - 3
\end{array} \right.\\
6)\left| {2{x^2} + 8x + 1} \right| = 4x + 17\\
\to \left[ \begin{array}{l}
2{x^2} + 8x + 1 = 4x + 17\\
2{x^2} + 8x + 1 = - 4x - 17
\end{array} \right.\\
\to \left[ \begin{array}{l}
2{x^2} + 4x - 16 = 0\\
2{x^2} + 12x + 18 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 2\\
x = - 4\\
x = - 3
\end{array} \right.\\
7)\left| {4{x^2} - 20x + 17} \right| = - 3{x^2} + 15x - 11\\
\to \left[ \begin{array}{l}
4{x^2} - 20x + 17 = - 3{x^2} + 15x - 11\\
4{x^2} - 20x + 17 = 3{x^2} - 15x + 11
\end{array} \right.\\
\to \left[ \begin{array}{l}
7{x^2} - 35x + 28 = 0\\
{x^2} - 5x + 6 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 4\\
x = 1\\
x = 3\\
x = 2
\end{array} \right.
\end{array}\)
