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Q31E

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Linear Algebra and its Applications
Found in: Page 191
Linear Algebra and its Applications

Linear Algebra and its Applications

Book edition 5th
Author(s) David C. Lay, Steven R. Lay and Judi J. McDonald
Pages 483 pages
ISBN 978-03219822384

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Short Answer

Verify that rank \({{\mathop{\rm uv}\nolimits} ^T} \le 1\) if \({\mathop{\rm u}\nolimits} = \left[ {\begin{array}{*{20}{c}}2\\{ - 3}\\5\end{array}} \right]\) and \({\mathop{\rm v}\nolimits} = \left[ {\begin{array}{*{20}{c}}a\\b\\c\end{array}} \right]\).

It is verified that rank \({{\mathop{\rm uv}\nolimits} ^T} \le 1\).

See the step by step solution

Step by Step Solution

Step 1: Compute the matrix \({{\mathop{\rm uv}\nolimits} ^T}\)

Compute the matrix \({{\mathop{\rm uv}\nolimits} ^T}\) as shown below:

\(\begin{aligned} {{\mathop{\rm uv}\nolimits} ^T} &= \left[ {\begin{array}{*{20}{c}}2\\{ - 3}\\5\end{array}} \right]\left[ {\begin{array}{*{20}{c}}a&b&c\end{array}} \right]\\ &= \left[ {\begin{array}{*{20}{c}}{2a}&{2b}&{2c}\\{ - 3a}&{ - 3b}&{ - 3c}\\{5a}&{5b}&{5c}\end{array}} \right]\end{aligned}\)

Step 2: Verify that rank \({{\mathop{\rm uv}\nolimits} ^T} \le 1\)

Each column of the matrix \({{\mathop{\rm uv}\nolimits} ^T}\)is a multiple of \({\mathop{\rm u}\nolimits} \).

\(\dim {\mathop{\rm Col}\nolimits} {{\mathop{\rm uv}\nolimits} ^T} = 1\) except when \(a = b = c = 0\) in which \({{\mathop{\rm uv}\nolimits} ^T}\) is a \(3 \times 3\) zero matrix. This means, \(\dim {\mathop{\rm Col}\nolimits} {{\mathop{\rm uv}\nolimits} ^T} = 0\).

However, rank \({{\mathop{\rm uv}\nolimits} ^T} = \dim {\mathop{\rm Col}\nolimits} {{\mathop{\rm uv}\nolimits} ^T} \le 1\).

Thus, it is verified that rank \({{\mathop{\rm uv}\nolimits} ^T} \le 1\).

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