Linear algebra: cofactors, signed minors

The tutor defines cofactor (aka signed minor) with an example.

In my post from Nov 24, 2014 I tell how to evaluate a determinant by hand.

Example: Evaluate the determinant of matrix A:

1 0 -7
0 2 1
3 1 0

If the determinant is calculated from the top row, as follows


we get

1[-1] + 0[3] -7[-6]

The numbers in red are called the cofactors or signed minors.

Cofactor Cmn is calculated as follows:

  1. Remove row m and column n.
  2. Calculate the determinant of the resultant matrix.
  3. Multiply that number by (-1)m+n

For every term in the matrix there is a signed minor.

I’ll be talking more about this:)


Johnson/Reiss/Arnold. Introduction to Linear Algebra. Don Mills: Addison-Wesley, 1989.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

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