Algebra II Recipe: Multiplying Matrices

A. Steps for A•B

1. The number of columns in matrix A must be equal to the number of rows in matrix B.
2. Multiply the entries in row 1 of matrix A by the entries in column 1 of matrix B, add the products and the result goes in row 1 column 1 of answer.
3. Multiply row 1 of matrix A by column 2 of matrix B, add the products and the result goes in row 1 column 2 of answer.
4. Continue until row 1 of matrix A has been multiplied by every column of matrix B.
5. Multiply row 2 of matrix A by every column of matrix B.
6. Continue until you have used each row in matrix A.
7. Matrix multiplication is not commutative. AB ¹ BA

Practice Problems