Question

Given matrix A below, calculate det[A] twice using minors and cofactors


`A = \left[\begin{array}{ccc}1&2&3\\3&4&5\\6&7&8\end{array}\right]`

Pivot on:
a) row 2, and also
b) column 3

Answer 1

a. 3(16-21) - 4(8-18) +5(7-12) = -15 + 40 - 25 = 0

b. 3(21-24) - 5(7-12) + 8(4-6) = -9 + 25 - 16 = 0