Question

Using words, state what two types of matrix multiplications are always commutative.

Answer 1

When we do multiplication:

• The number of columns of the 1st matrix must equal the number of rows of the 2nd matrix. And the result will have the same number of rows as the 1st matrix, and the same number of columns as the 2nd matrix.

• To multiply an m×n matrix by an n×p matrix, the ns must be the same,
  and the result is an m×p matrix.

  

So to be commulative both matrix should be square matrix , because square matrix have equal number of row and columns .