将平面上任意向量[mathjaxinline]\left(\begin{matrix}x\\y\end{matrix}\right)[/mathjaxinline]逆时针旋转90度, 得到[mathjaxinline]\left(\begin{matrix}x'\\y'\end{matrix}\right)[/mathjaxinline], 则(x', y')=____.
A. (y, x)
B. (y, -x)
C. (-y, x)
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[mathjaxinline]A = \left(\begin{matrix}1&0&0&-1\\-1&1&0&0\\0&-1&1&0\\0&0&-1&1\end{matrix}\right)[/mathjaxinline], 问A是否可逆?
A. 是
B. 否
[mathjaxinline]A = \left(\begin{matrix}1&0&c \\1&1&0 \\0&1&1\end{matrix}\right)[/mathjaxinline], c为何值时, A不可逆?
A. 1
B. -1
C. 0
设线性方程组[mathjaxinline]\begin{pmatrix} a & 1 & 1 \\ 1 & a & 1 \\ 1 & 1 & a \end{pmatrix} \begin{pmatrix} x_1 \\ x_2 \\ x_3 \end{pmatrix} = \begin{pmatrix} 1 \\ 1 \\ -2 \end{pmatrix} [/mathjaxinline]有无穷多个解,则[mathjaxinline]a = [/mathjaxinline] ____
A. 1
B. 3
C. -1
D. -2
令[mathjaxinline] \mathbf{w}_1 = \begin{pmatrix} 1 \\ 2 \\ 3 \end{pmatrix}, \mathbf{w}_2 = \begin{pmatrix} 4 \\ 5 \\ 6 \end{pmatrix}, \mathbf{w}_3 = \begin{pmatrix} 7 \\ 8 \\ 9 \end{pmatrix}, [/mathjaxinline] 则[mathjaxinline] (x_1, x_2, x_3) =[/mathjaxinline]____时,有[mathjaxinline] x_1\mathbf{w}_1+x_2\mathbf{w}_2+x_3\mathbf{w}_3 = 0[/mathjaxinline]?
A. [mathjaxinline] (-\frac{1}{2}, -1, \frac{1}{2}) [/mathjaxinline]
B. [mathjaxinline] (\frac{3}{2}, -2, \frac{1}{2}) [/mathjaxinline]
C. [mathjaxinline] (\frac{1}{2}, -1, \frac{1}{2}) [/mathjaxinline]
D. [mathjaxinline] (0, -\frac{3}{2}, \frac{1}{2}) [/mathjaxinline]