题目
beta_1 = alpha_1, beta_2 = alpha_1 + alpha_2, beta_3 = alpha_1 + alpha_2 + alpha_3, 记A = [alpha_1, alpha_2, alpha_3], B = [beta_1, beta_2, beta_3], 则B=AC,那么矩阵C为 A. } 1 & 0 & 0 1 & 1 & 0 1 & 1 & 1 ,B. } 1 & 1 & 1 0 & 0 & 1 0 & 0 & 1 ,C. } 0 & 0 & 1 0 & 1 & 1 1 & 1 & 1 ,D. } 1 & 1 & 1 0 & 1 & 1 0 & 0 & 1 .
$\beta_1 = \alpha_1$, $\beta_2 = \alpha_1 + \alpha_2$, $\beta_3 = \alpha_1 + \alpha_2 + \alpha_3$, 记A = $[\alpha_1, \alpha_2, \alpha_3]$, B = $[\beta_1, \beta_2, \beta_3]$, 则B=AC,那么矩阵C为
- A. $\begin{bmatrix} 1 & 0 & 0 \\ 1 & 1 & 0 \\ 1 & 1 & 1 \end{bmatrix}$,
- B. $\begin{bmatrix} 1 & 1 & 1 \\ 0 & 0 & 1 \\ 0 & 0 & 1 \end{bmatrix}$,
- C. $\begin{bmatrix} 0 & 0 & 1 \\ 0 & 1 & 1 \\ 1 & 1 & 1 \end{bmatrix}$,
- D. $\begin{bmatrix} 1 & 1 & 1 \\ 0 & 1 & 1 \\ 0 & 0 & 1 \end{bmatrix}$.
题目解答
答案
为了确定矩阵 $ C $ 使得 $ B = AC $,我们需要将 $ B $ 的列用 $ A $ 的列表示。已知 $ \beta_1 = \alpha_1 $, $ \beta_2 = \alpha_1 + \alpha_2 $,和 $ \beta_3 = \alpha_1 + \alpha_2 + \alpha_3 $,我们可以写成:
\[
B = [\beta_1, \beta_2, \beta_3] = [\alpha_1, \alpha_1 + \alpha_2, \alpha_1 + \alpha_2 + \alpha_3]
\]
我们希望将 $ B $ 表示为 $ AC $ 的形式,其中 $ A = [\alpha_1, \alpha_2, \alpha_3] $。这意味着我们需要找到一个矩阵 $ C $ 使得:
\[
[\alpha_1, \alpha_1 + \alpha_2, \alpha_1 + \alpha_2 + \alpha_3] = [\alpha_1, \alpha_2, \alpha_3] \begin{bmatrix} c_{11} & c_{12} & c_{13} \\ c_{21} & c_{22} & c_{23} \\ c_{31} & c_{32} & c_{33} \end{bmatrix}
\]
通过矩阵乘法,右边变为:
\[
[\alpha_1, \alpha_2, \alpha_3] \begin{bmatrix} c_{11} & c_{12} & c_{13} \\ c_{21} & c_{22} & c_{23} \\ c_{31} & c_{32} & c_{33} \end{bmatrix} = [\alpha_1 c_{11} + \alpha_2 c_{21} + \alpha_3 c_{31}, \alpha_1 c_{12} + \alpha_2 c_{22} + \alpha_3 c_{32}, \alpha_1 c_{13} + \alpha_2 c_{23} + \alpha_3 c_{33}]
\]
我们需要这个等于 $ [\alpha_1, \alpha_1 + \alpha_2, \alpha_1 + \alpha_2 + \alpha_3] $。因此,我们可以将对应的列的系数相等:
1. 对于第一列: $ \alpha_1 c_{11} + \alpha_2 c_{21} + \alpha_3 c_{31} = \alpha_1 $
- 这给出 $ c_{11} = 1 $, $ c_{21} = 0 $,和 $ c_{31} = 0 $。
2. 对于第二列: $ \alpha_1 c_{12} + \alpha_2 c_{22} + \alpha_3 c_{32} = \alpha_1 + \alpha_2 $
- 这给出 $ c_{12} = 1 $, $ c_{22} = 1 $,和 $ c_{32} = 0 $。
3. 对于第三列: $ \alpha_1 c_{13} + \alpha_2 c_{23} + \alpha_3 c_{33} = \alpha_1 + \alpha_2 + \alpha_3 $
- 这给出 $ c_{13} = 1 $, $ c_{23} = 1 $,和 $ c_{33} = 1 $。
因此,矩阵 $ C $ 是:
\[
C = \begin{bmatrix} 1 & 1 & 1 \\ 0 & 1 & 1 \\ 0 & 0 & 1 \end{bmatrix}
\]
正确答案是 $\boxed{D}$。