Elementary Linear Algebra 7th Edition

Published by Cengage Learning
ISBN 10: 1-13311-087-8
ISBN 13: 978-1-13311-087-3

Chapter 3 - Determinants - 3.3 Properties of Determinants - 3.3 Exercises - Page 127: 69

Answer

The statement is correct.

Work Step by Step

Since the matrix $A$ is a square matrix of order $n$ and a skew-symmetric matrix, then $A^{T}=-A$ . Let the general form of the matrix $A$ be as follows $A=\left[\begin{array}{ccccc} a_{11} & a_{12} & & & & a_{1n} \\ a_{21} & a_{22} & & .. & & a_{2n} \\ & . & . & . & &. \\ & & && . & . \\ a_{n1} & a_{n2} & . &&& a_{nn} \\ \end{array}\right]$ Since $|A^{T}|=|A|$, using the assumption $A^{T}=-A$, we obtain $|-A|=|A|$ and then we have $|A|= |-A|=\left|\begin{array}{ccccc} -a_{11} & -a_{12} & & & & -a_{1n} \\ -a_{21} & -a_{22} & & .. & & -a_{2n} \\ & . & . & . & &. \\ & & && . & . \\ -a_{n1} & -a_{n2} & . &&& -a_{nn} \\ \end{array}\right|$ By taking the common factor $(-1)$ of $n$ rows of the determinant $|-A|$, we have $|A|=|-A|=(-1)(-1)(-1) (-1) * \left|\begin{array}{ccccc} a_{11} & a_{12} & & & & a_{1n} \\ a_{21} & a_{22} & & .. & & a_{2n} \\ & . & . & . & &. \\ & & && . & . \\ a_{n1} & a_{n2} & . &&& a_{nn} \\ \end{array}\right|=(-1)^{n}|A|$ Thus $|A|=(-1)^{n}|A|$
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