Compute the determinant by cofactor expansions.
A=
| 1 -2 5 2|
| 0 0 3 0|
| 2 -4 -3 5|
| 2 0 3 5|
I figured the easiest way to compute this problem would be to use a cofactor across row 2. So I got:
det A =
|-1 -2 2|
-3| 2 -4 5|
| 2 0 5|
I went on to factor across the third row.
det A =
( |-2 2| |-1 -2|)
-3(2|-4 5| + 5| 2 -4|)
det A = -3(2(-10+8)+5(4+4))
det A = -3(-4+40)
det A = -108
When I check my work on a determinate calculator I see that I should be getting det A = 12, but I can't seem to see where I'm messing up.
