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Q16Section ST (Statistics (Q11–Q65))16 of 65

Null space of a rank-one matrix

Let A=(a1a2a3 b1b2b3)A = \begin{pmatrix}a_1 & a_2 & a_3\ b_1 & b_2 & b_3\end{pmatrix} be a 2×32 \times 3 real matrix, where (a1,a2,a3)≠(0,0,0)(a_1,a_2,a_3) \ne (0,0,0) and (b1,b2,b3)≠(0,0,0)(b_1,b_2,b_3) \ne (0,0,0). Assume that the rank of AA is 1. Define the subspaces W={x=(x1x2x3)∈R3:Ax=0}W = \{\mathbf{x} = \begin{pmatrix}x_1\\x_2\\x_3\end{pmatrix}\in\mathbb{R}^3 : A\mathbf{x} = \mathbf{0}\}, W1={x=(x1x2x3)∈R3:a1x1+a2x2+a3x3=0}W_1 = \{\mathbf{x} = \begin{pmatrix}x_1\\x_2\\x_3\end{pmatrix}\in\mathbb{R}^3 : a_1x_1 + a_2x_2 + a_3x_3 = 0\} and W2={x=(x1x2x3)∈R3:b1x1+b2x2+b3x3=0}W_2 = \{\mathbf{x} = \begin{pmatrix}x_1\\x_2\\x_3\end{pmatrix}\in\mathbb{R}^3 : b_1x_1 + b_2x_2 + b_3x_3 = 0\}. Consider the following statements: (I) W=W1∩W2W = W_1 \cap W_2 (II) W1=W2W_1 = W_2 Which of the above statements is/are true?

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