Minor of aᵢⱼ is the determinant of the submatrix formed by deleting the ith row and jth column.
Minor is the determinant of a smaller square matrix, which results in a scalar.
Deleting one row and one column from a 3×3 matrix leaves a 2×2 submatrix.
Cofactor = (−1)^(i+j) × Minor; minor itself has no sign adjustment.
Deleting row 1 and column 1 leaves [4]; determinant = 4.
Deleting row 1 and column 1 leaves [[1,0],[2,1]], determinant = 1×1 − 0×2 = 1.
Deleting row and column of a diagonal element leaves another diagonal matrix; determinant = product of remaining diagonal entries.
Each of the 9 elements has its own minor, so there are 9 minors.
Cofactor = signed minor; not every minor is a cofactor.
Determinants of larger matrices are expanded using minors (Laplace expansion).