In Exercises 27 - 36, find (if possible) the following matrices: a. AB b. BA 1 3 3 - 2 A = B = 5 3 - 1 6
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Introduction to Matrices
Problem 39
Textbook Question
In Exercises 37 - 44, perform the indicated matrix operations given that A, B and C are defined as follows. If an operation is not defined, state the reason. 4 0 5 1 1 - 1 A = - 3 5 B = C = 0 1 - 2 - 2 - 1 1 BC + CB
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Identify the dimensions of matrices B and C to determine if the products BC and CB are defined. Matrix B has dimensions 2x3 (2 rows, 3 columns), and matrix C has dimensions 3x2 (3 rows, 2 columns).
Check if the product BC is defined: Since B is 2x3 and C is 3x2, the inner dimensions (3 and 3) match, so BC is defined and will result in a 2x2 matrix.
Check if the product CB is defined: Since C is 3x2 and B is 2x3, the inner dimensions (2 and 2) match, so CB is defined and will result in a 3x3 matrix.
Since BC is a 2x2 matrix and CB is a 3x3 matrix, the sum BC + CB is not defined because matrix addition requires both matrices to have the same dimensions.
Conclude that the operation BC + CB is not defined due to incompatible dimensions for addition.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Matrix Multiplication
Matrix multiplication involves multiplying rows of the first matrix by columns of the second matrix and summing the products. It is only defined when the number of columns in the first matrix equals the number of rows in the second. The order of multiplication matters, as AB generally does not equal BA.
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Matrix Addition
Matrix addition requires two matrices of the same dimensions. Corresponding elements are added together to form a new matrix. This operation is commutative, meaning A + B equals B + A, and is straightforward once the matrices have compatible sizes.
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Dimension Compatibility for Operations
Before performing matrix operations, it is essential to check the dimensions of the matrices involved. For multiplication, the inner dimensions must match; for addition, the matrices must have identical dimensions. If these conditions are not met, the operation is undefined.
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