设矩阵 $\boldsymbol{A}=\left(\begin{array}{cc}2 & 1 \\ -1 & 2\end{array}\right), \boldsymbol{E}$ 为 2 阶单位矩阵, 矩阵 $\boldsymbol{B}$ 满足 $\boldsymbol{B} \boldsymbol{A}=\boldsymbol{B}+2 \boldsymbol{E}$, 则 $|\boldsymbol{B}|=$
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