Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 3 - Determinants - 3.1 The Definition of the Determinant - Problems - Page 207: 26

Answer

\begin{aligned} \operatorname{det}(A)&=\left|\begin{array}{ccc}{5} & {-3} & {0} \\ {1} & {4} & {-1} \\ {-8} & {2} & {-2}\end{array}\right|=-60 \end{aligned}

Work Step by Step

Given $$ A=\left[\begin{array}{ccc}{5} & {-3} & {0} \\ {1} & {4} & {-1} \\ {-8} & {2} & {-2}\end{array}\right]$$ Since, if we have$$A=\left[\begin{array}{lll}{a_{11}} & {a_{12}} & {a_{13}} \\ {a_{21}} & {a_{22}} & {a_{23}} \\ {a_{31}} & {a_{32}} & {a_{33}}\end{array}\right]$$ we get \begin{aligned}\operatorname{det}(A)&=\left|\begin{array}{lll}{a_{11}} & {a_{12}} & {a_{13}} \\ {a_{21}} & {a_{22}} & {a_{23}} \\ {a_{31}} & {a_{32}} & {a_{33}}\end{array}\right|\\ &=a_{11}\left|\begin{array}{ll} {a_{22}} & {a_{23}} \\ {a_{32}} & {a_{33}}\end{array}\right|-a_{12}\left|\begin{array}{ll} {a_{21}} & {a_{23}} \\ {a_{31}} & {a_{33}}\end{array}\right|+a_{13}\left|\begin{array}{ll} {a_{21}} & {a_{22}} \\ {a_{31}} & {a_{32}}\end{array}\right|\\ &=a_{11}( a_{22} a_{33}-a_{23} a_{32})-a_{12}( a_{21} a_{33}-a_{23} a_{31})+a_{13}( a_{21} a_{32}-a_{22} a_{31})\\ &=a_{11} a_{22} a_{33}+a_{12} a_{23} a_{31}+a_{13} a_{21} a_{32}-a_{11} a_{23} a_{32}-a_{12} a_{21} a_{33}-a_{13} a_{22} a_{31}\\ \end{aligned} Therefore, we get \begin{aligned} \operatorname{det}(A)&=\left|\begin{array}{ccc}{5} & {-3} & {0} \\ {1} & {4} & {-1} \\ {-8} & {2} & {-2}\end{array}\right|\\ &=5 \cdot 4 \cdot(-2)+(-3) \cdot(-1) \cdot(-8)+0 \cdot 1 \cdot 2-5 \cdot(-1) \cdot 2-(-3) \cdot 1 \cdot(-2)-0 \cdot 4 \cdot(-8)\\ &=-40-24+0+10-6+0\\ &=-60 \end{aligned}
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