Final answer:
To sum two matrices, they must be of the same size, meaning the number of rows and columns in each matrix should be identical. If their sizes differ, the sum cannot be performed.
Step-by-step explanation:
For two matrices, a and b, to be summed, they must be of the same size. This means that the number of rows and columns in matrix a must be equal to the number of rows and columns in matrix b. If these conditions are not met, the sum of matrices a and b is undefined and therefore cannot be performed.
Example:
Let's say matrix a is a 2x3 matrix (2 rows and 3 columns) and matrix b is also a 2x3 matrix. The sum of these matrices is possible because their sizes are identical. On the other hand, if matrix a remains a 2x3 matrix but matrix b is a 3x2 matrix, their sum would not be possible as the matrices are of different sizes.