Question

$\left[\begin{array}{ccc}5&0&1\\3&2&-4\\-2&6&1\end{array}\right]$

Calcule (A.A) 

Answer 1

5   0     1  5  0
3   2   - 4  3  2
-2  6     1 -2  6

DP= 5.2.1+0.(-4)(-2)+1.3.6=10+0+18=28
DS= 0.3.1+5.(-4).6+1.2(-2)=0-120-4= - 124

det A= DP - DS

detA = 28 - (- 124)

detA= 28 + 124

detA = 152