Given:
The matrix multiplication
To find:
The order of resulting matrix.
Solution:
We know that, if order of first matrix is and the order of second matrix is , then the order of these two matrices is .
We have,
Here, the order of first matrix is and the order of the second matrix is . So, the order of the second matrix is . It is also written are 2 by 1.
Therefore, the correct option is A.