Final answer:
The missing words in the question are likely 'invertible' and 'defined'. The size of matrix B is determined by the dimensions of matrix A.
Step-by-step explanation:
The question is missing some essential information, but based on the available details, we can deduce that the missing word in the first blank is 'invertible' or 'non-singular', indicating that the matrix A has an inverse or is non-singular. The missing word in the second blank could be 'defined', 'valid', or 'computable', indicating that the product AB is defined or valid.
Given that A is invertible and AB is defined, the size or dimensions of matrix B can be determined by examining the compatibility condition for matrix multiplication. The number of columns in A must be equal to the number of rows in B. So if matrix A is m x n, then matrix B must be n x p, where 'n' represents the number of columns in matrix A and 'p' represents the number of columns in matrix B.