\(\begin{array}{l}
9)\,\sqrt {{x^2}} = x\,\,\,DK:\,x \ge 0\\
{x^2} = {x^2}\,\left( {luon\,dung} \right)\\
Vay\,x \ge 0\\
\sqrt {{x^2}} = - x\,\,DK: - x \ge 0 \Rightarrow x \le 0\\
{x^2} = {\left( { - x} \right)^2}\\
{x^2} = {x^2}\,\,\left( {luon\,dung} \right)\\
Vay\,\,x \le 0\\
x\sqrt {x - 2} = 0\\
\Rightarrow \left[ \begin{array}{l}
x = 0\\
\sqrt {x - 2} = 0
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = 0\\
x = 2
\end{array} \right.\\
\left( {{x^2} - 4} \right)\sqrt x = 0\\
\Rightarrow \left[ \begin{array}{l}
{x^2} - 4 = 0\\
\sqrt x = 0
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
{x^2} = 4\\
x = 0
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = 2\\
x = - 2\\
x = 0
\end{array} \right.\\
10)\,\,A = \left( {\frac{1}{4} - \frac{{13}}{{36}}.9} \right):\left( {\frac{2}{3} + \frac{7}{{15}}.\frac{{30}}{7}} \right)\\
= \left( {\frac{1}{4} - \frac{{13}}{4}} \right):\left( {\frac{2}{3} + 2} \right) = \left( { - 3} \right):\frac{8}{3} = - \frac{1}{8}\\
B = \left( {5,6 + 0,64} \right).\left( {8,75 - 1} \right) + 31,64\\
= 6,24.7,75 + 31,64 = 48,36 + 31,64 = 80
\end{array}\)
