A cofactor is basically a one-size smaller "sub-determinant" of the full determinant of a matrix, with an appropriate sign attached. On the following pages, you'll see:
  1. What a minor and a cofactor of a determinant are,
  2. How to calculate determinants using cofactors,
  3. How to find matrix inverses using cofactors.
Prerequisites. You should understand the basic definition of a determinant and how to use row and column operations to calculate it. (See the learning object The Formal Definition of a Determinant for details.) For the last page, you should also know what the inverse of a matrix is, and that it exists only when the matrix has a non-zero determinant.
Keywords: determinant, Laplace expansion, minor, cofactor, adjoint of a matrix, inverse of a matrix
Minors, Cofactors and the Laplace Expansion of Determinants
Introduction Minors and cofactors The Laplace expansion of a determinant Adjoints and inverses of matrices