Multiplication of two matrices possible if the number of columns in the first matrix equals the number of rows in the second matrix.
\The dimensions of the matrix X are
and the number of columns in the matrix X is 6.
The dimensions of the matrix Y are
and the number of the rows in the matrix Y is 6.
The number of columns in the matrix X equals the number of rows in the matrix Y.
\So, matrix product XY is possible.
\Its dimensions are
.

The matrix product XY is defined and matrix XY dimensions are
.