Bài giải:

Giải:+) $\left( 2x-{{x}^{2}} \right)\left( 2{{x}^{2}}-3x-2 \right)=0$

$\Rightarrow \left[ \begin{align}& 2x-{{x}^{2}}=0 \\ & 2{{x}^{2}}-3x-2=0 \\\end{align} \right.$

$\Rightarrow \left[ \begin{align}& x\left( 2-x \right)=0 \\ & \left( x-2 \right)\left( 2x+1 \right)=0 \\ \end{align} \right.$

$\Rightarrow \left[ \begin{align}& x=0 \\ & x=2 \\ & x=-\frac{1}{2} \\\end{align} \right.$

$\Rightarrow A=\left\{ -\frac{1}{2};0;2 \right\}$

+) $3<{{n}^{2}}<30$ $\Rightarrow n=\left\{ 2;3;4;5 \right\}$

$\Rightarrow B=\left\{ 2;3;4;5 \right\}$

$A\cap B=\left\{ 2 \right\}$

Đáp án đúng là B