Given, $A$ is $3 \times 4$ matrix. So, $A'$ is $4 \times 3$ matrix. Since, $A' B$ is defined, therefore $B$ should he $3 \times 4.$ Also, $B A'$ is defined, so $B$ should be $3 \times 4$. Hence, $B$ is of the type $3 \times 4$
A matrix is a rectangular array of numbers, variables, symbols, or expressions that are defined for the operations like subtraction, addition, and multiplications. The size of a matrix is determined by the number of rows and columns in the matrix.
The basic operations that can be performed on matrices are:
Addition of Matrices - The addition of matrices addition can only be possible if the number of rows and columns of both the matrices are the same.
Subtraction of Matrices - Matrices subtraction is also possible only if the number of rows and columns of both the matrices are the same.
Scalar Multiplication - The product of a matrix A with any number 'c' is obtained by multiplying every entry of the matrix A by c, is called scalar multiplication.
Multiplication of Matrices - Matrices multiplication is defined only if the number of columns in the first matrix and rows in the second matrix are equal.
Transpose of Matrices - Interchanging of rows and columns is known as the transpose of matrices.