Question

Find all (a) minors and (b) cofactors of the matrix
[ -3 2 -8 ]
3 -2 6
-1 3 -6

Answer 1

minors and cofactors are simple; just follow the rules. I'll do the ones for [1;1]

minor: remove row 1 and column 1:
[-2 6]
[3 -6]

cofactor: add the index of the row and column, and use that as an exponent of -1, then multiply the minor by that:

(-1)^(1+1) = (-1)^2 = 1

so, the cofactor is just the same as the minor for [1;1]

As you go along each row and column, the sign of the cofactor changes.