# Difference between revisions of "Cofactor (mathematics)"

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In mathematics, a cofactor is a component of a matrix computation of the matrix determinant.

Let M be a square matrix of size n. The (i,j) minor refers to the determinant of the (n-1)×(n-1) submatrix Mi,j formed by deleting the i-th row and j-th column from M (or sometimes just to the submatrix Mi,j itself). The corresponding cofactor is the signed determinant



The adjugate matrix adj M is the square matrix whose (i,j) entry is the (j,i) cofactor. We have



which encodes the rule for expansion of the determinant of M by any the cofactors of any row or column. This expression shows that if det M is invertible, then M is invertible and the matrix inverse is determined as



## Example

Consider the following example matrix,



Its minors are the determinants (bars indicate a determinant):




The adjugate matrix of M is



and the inverse matrix is



Indeed,



and the other matrix elements of the product follow likewise.