Đáp án:
a)$S = \left( { - \infty ; - 2} \right) \cup \left( { - 2;1} \right) \cup \left( {3; + \infty } \right)$
b)$S = \left( { - \infty ; - 4} \right) \cup \left( {0; + \infty } \right)$
c)$S = \left( { - \infty ;0} \right) \cup \left( {2; + \infty } \right)$
d)$S = \left( { - \infty ;0} \right) \cup \left( {3 + \sqrt 6 ; + \infty } \right) \cup \left( {3 - \sqrt 6 ;2} \right) \cup \left( {1;2} \right)$
Giải thích các bước giải:
$\begin{array}{l}
a)\left| {{x^2} - 4} \right| > x + 2\\
\Leftrightarrow \left[ \begin{array}{l}
x + 2 < 0\\
\left\{ \begin{array}{l}
x + 2 \ge 0\\
\left[ \begin{array}{l}
{x^2} - 4 > x + 2\\
{x^2} - 4 < - x - 2
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < - 2\\
\left\{ \begin{array}{l}
x \ge - 2\\
\left[ \begin{array}{l}
{x^2} - x - 6 > 0\\
{x^2} + x - 2 < 0
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < - 2\\
\left\{ \begin{array}{l}
x \ge - 2\\
\left[ \begin{array}{l}
x > 3\\
x < - 2\\
- 2 < x < 1
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < - 2\\
x > 3\\
- 2 < x < 1
\end{array} \right.
\end{array}$
Vậy tập nghiệm của bất phương trình là: $S = \left( { - \infty ; - 2} \right) \cup \left( { - 2;1} \right) \cup \left( {3; + \infty } \right)$
$\begin{array}{l}
b)2\left| {x + 3} \right| - x - 6 > 0\\
\Leftrightarrow 2\left| {x + 3} \right| > x + 6\\
\Leftrightarrow \left[ \begin{array}{l}
x + 6 < 0\\
\left\{ \begin{array}{l}
x + 6 \ge 0\\
\left[ \begin{array}{l}
2\left( {x + 3} \right) > x + 6\\
2\left( {x + 3} \right) < - x - 6
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < - 6\\
\left\{ \begin{array}{l}
x \ge - 6\\
\left[ \begin{array}{l}
x > 0\\
x < - 4
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < - 6\\
x > 0\\
- 6 \le x < - 4
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x > 0\\
x < - 4
\end{array} \right.
\end{array}$
Vậy tập nghiệm của bất phương trình là: $S = \left( { - \infty ; - 4} \right) \cup \left( {0; + \infty } \right)$
$\begin{array}{l}
c)\left| {{x^2} + 3x + 2} \right| - 2x + {x^2} > 0\\
\Leftrightarrow \left| {{x^2} + 3x + 2} \right| > - {x^2} + 2x\\
\Leftrightarrow \left[ \begin{array}{l}
- {x^2} + 2x < 0\\
\left\{ \begin{array}{l}
- {x^2} + 2x \ge 0\\
\left[ \begin{array}{l}
{x^2} + 3x + 2 > - {x^2} + 2x\\
{x^2} + 3x + 2 < {x^2} - 2x
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
\left[ \begin{array}{l}
x > 2\\
x < 0
\end{array} \right.\\
\left\{ \begin{array}{l}
0 \le x \le 2\\
\left[ \begin{array}{l}
2{x^2} + x + 2 > 0\left( {ld} \right)\\
5x + 2 < 0
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x > 2\\
x < 0\\
\left\{ \begin{array}{l}
0 \le x \le 2\\
x < \dfrac{{ - 2}}{5}
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x > 2\\
x < 0
\end{array} \right.
\end{array}$
Vậy tập nghiệm của bất phương trình là: $S = \left( { - \infty ;0} \right) \cup \left( {2; + \infty } \right)$
$\begin{array}{l}
d)\left| {\dfrac{{4x - 3}}{{x - 2}}} \right| > x\left( {DK:x \ne 2} \right)\\
\Leftrightarrow \left[ \begin{array}{l}
x < 0\\
\left\{ \begin{array}{l}
x \ge 0\\
\left[ \begin{array}{l}
\dfrac{{4x - 3}}{{x - 2}} > x\\
\dfrac{{4x - 3}}{{x - 2}} < - x
\end{array} \right.
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x < 0\\
\left\{ \begin{array}{l}
x \ge 0\\
\left[ \begin{array}{l}
\dfrac{{ - {x^2} + 6x - 3}}{{x - 2}} > 0\\
\dfrac{{{x^2} + 2x - 3}}{{x - 2}} < 0
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < 0\\
\left\{ \begin{array}{l}
x \ge 0\\
\left[ \begin{array}{l}
\left\{ \begin{array}{l}
- {x^2} + 6x - 3 > 0\\
x - 2 > 0
\end{array} \right.\\
\left\{ \begin{array}{l}
- {x^2} + 6x - 3 < 0\\
x - 2 < 0
\end{array} \right.\\
\left\{ \begin{array}{l}
{x^2} + 2x - 3 > 0\\
x - 2 < 0
\end{array} \right.\\
\left\{ \begin{array}{l}
{x^2} + 2x - 3 < 0\\
x - 2 > 0
\end{array} \right.
\end{array} \right.
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x < 0\\
\left\{ \begin{array}{l}
x \ge 0\\
\left[ \begin{array}{l}
\left\{ \begin{array}{l}
\left[ \begin{array}{l}
x > 3 + \sqrt 6 \\
x < 3 - \sqrt 6
\end{array} \right.\\
x > 2
\end{array} \right.\\
\left\{ \begin{array}{l}
3 - \sqrt 6 < x < 3 + \sqrt 6 \\
x < 2
\end{array} \right.\\
\left\{ \begin{array}{l}
\left[ \begin{array}{l}
x > 1\\
x < - 3
\end{array} \right.\\
x < 2
\end{array} \right.\\
\left\{ \begin{array}{l}
- 3 < x < 1\\
x > 2
\end{array} \right.\left( {vn} \right)
\end{array} \right.
\end{array} \right.
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x < 0\\
\left\{ \begin{array}{l}
x \ge 0\\
\left[ \begin{array}{l}
x > 3 + \sqrt 6 \\
3 - \sqrt 6 < x < 2\\
1 < x < 2\\
x < - 3
\end{array} \right.
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x < 0\\
x > 3 + \sqrt 6 \\
3 - \sqrt 6 < x < 2\\
1 < x < 2
\end{array} \right.
\end{array}$
Vậy tập nghiệm của bất phương trình là: $S = \left( { - \infty ;0} \right) \cup \left( {3 + \sqrt 6 ; + \infty } \right) \cup \left( {3 - \sqrt 6 ;2} \right) \cup \left( {1;2} \right)$