Linear Algebra and Its Applications (5th Edition)

Published by Pearson
ISBN 10: 032198238X
ISBN 13: 978-0-32198-238-4

Chapter 3 - Determinants - Supplementary Exercises - Page 188: 6

Answer

12

Work Step by Step

Let \[A=\left|\begin{array}{ccccc} 4&8&8&8&5\\ 0&1&0&0&0\\ 6&8&8&8&7\\ 0&8&8&3&0\\ 0&8&2&0&0\end{array}\right|\] Expanding determinant $A$ along 2nd row \[A=(-1)^{2+2} \left|\begin{array}{cccc}4&8&8&5\\ 6&8&8&7\\ 0&8&3&0\\ 0&2&0&0\end{array}\right|\] \[A= \left|\begin{array}{cccc}4&8&8&5\\ 6&8&8&7\\ 0&8&3&0\\ 0&2&0&0\end{array}\right|\] Again expanding along 4th row \[A=(-1)^{4+2}(2) \left|\begin{array}{ccc}4&8&5\\ 6&8&7\\ 0&3&0\\\end{array}\right|\] \[A=(2) \left|\begin{array}{ccc}4&8&5\\ 6&8&7\\ 0&3&0\\\end{array}\right|\] Again expanding along 3th row \[A=(2)(-3)[(4)(7)-(5)(6)]\] \[A=(-6)[28-30]\] \[A=(-6)(-2)=12\] Hence $A=12$.
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