The solution of the second-order matrix
is a1 b2 − a2 b1.
The solution of the third-order matrix
is
a1, a2, . . ., c2, c3 are called the elements of the matrix.
The lower order matrix associated with a1, that is
is called the cofactor of a1, denoted A1. Similarly,
is the cofactor of b1, denoted B1, and so on. Thus the solution of the third order matrix is
a1A1 + b1B1 + c1C1
and so on for higher orders.
To get the cofactor signs correct, think of the element positions in the matrix as having positive and negative signs associated with them, as follows:
Matrix multiplication