Final answer:
If the first two columns B1 and B2 of matrix B are equal, then the columns of AB will also be equal.
Step-by-step explanation:
If the first two columns B1 and B2 of matrix B are equal, then it means that the entries in those two columns are the same. When we perform matrix multiplication AB, each column of AB is a linear combination of the columns of B using the corresponding entries in the rows of A. Since the first two columns of B are the same, this means that the linear combinations used to form each column of AB will be the same as well. Therefore, the columns of AB will be equal.