Let $A=\left[\begin{array}{lll}2 & 0 & 1 \\ 1 & 1 & 0 \\ 1 & 0 & 1\end{array}\right], B=\left[B_1, B_2, B_3\right]$, where $B_1, B_2, B_3$ are column matrics, and
$$
\mathrm{AB}_1=\left[\begin{array}{l}
1 \\
0 \\
0
\end{array}\right], \mathrm{AB}_2=\left[\begin{array}{l}
2 \\
3 \\
0
\end{array}\right], \quad \mathrm{AB}_3=\left[\begin{array}{l}
3 \\
2 \\
1
\end{array}\right]
$$
If $\alpha=|B|$ and $\beta$ is the sum of all the diagonal elements of $B$, then $\alpha^3+\beta^3$ is equal to ____________.
Answer (integer)
28
Solution
<p>$$\mathrm{A}=\left[\begin{array}{lll}
2 & 0 & 1 \\
1 & 1 & 0 \\
1 & 0 & 1
\end{array}\right] \quad \mathrm{B}=\left[\mathrm{B}_1, \mathrm{~B}_2, \mathrm{~B}_3\right]$$</p>
<p>$$\mathrm{B}_1=\left[\begin{array}{l}
\mathrm{x}_1 \\
\mathrm{y}_1 \\
\mathrm{z}_1
\end{array}\right], \quad \mathrm{B}_2=\left[\begin{array}{l}
\mathrm{x}_2 \\
\mathrm{y}_2 \\
\mathrm{z}_2
\end{array}\right], \quad \mathrm{B}_3=\left[\begin{array}{l}
\mathrm{x}_3 \\
\mathrm{y}_3 \\
\mathrm{z}_3
\end{array}\right]$$</p>
<p>$$\mathrm{AB}_1=\left[\begin{array}{lll}
2 & 0 & 1 \\
1 & 1 & 0 \\
1 & 0 & 1
\end{array}\right]\left[\begin{array}{l}
\mathrm{x}_1 \\
\mathrm{y}_1 \\
\mathrm{z}_1
\end{array}\right]=\left[\begin{array}{l}
1 \\
0 \\
0
\end{array}\right]$$</p>
<p>$$\begin{gathered}
\mathrm{x}_1=1, \mathrm{y}_1=-1, \mathrm{z}_1=-1 \\
\mathrm{AB}_2=\left[\begin{array}{lll}
2 & 0 & 1 \\
1 & 1 & 0 \\
1 & 0 & 1
\end{array}\right]\left[\begin{array}{l}
\mathrm{x}_2 \\
\mathrm{y}_2 \\
\mathrm{z}_2
\end{array}\right]=\left[\begin{array}{l}
2 \\
3 \\
0
\end{array}\right] \\
\mathrm{x}_2=2, \mathrm{y}_2=1, \mathrm{z}_2=-2 \\
\mathrm{AB}_3=\left[\begin{array}{lll}
2 & 0 & 1 \\
1 & 1 & 0 \\
1 & 0 & 1
\end{array}\right]\left[\begin{array}{l}
\mathrm{x}_3 \\
\mathrm{y}_3 \\
\mathrm{z}_3
\end{array}\right]=\left[\begin{array}{l}
3 \\
2 \\
1
\end{array}\right] \\
\mathrm{x}_3=2, \mathrm{y}_3=0, \mathrm{z}_3=-1 \\
\mathrm{~B}=\left[\begin{array}{ccc}
1 & 2 & 2 \\
-1 & 1 & 0 \\
-1 & -2 & -1
\end{array}\right] \\
\alpha=|\mathrm{B}|=3 \\
\beta=1 \\
\alpha^3+\beta^3=27+1=28
\end{gathered}$$</p>
About this question
Subject: Mathematics · Chapter: Matrices and Determinants · Topic: Types of Matrices and Operations
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