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Ch. 5 - Systems and Matrices
Lial - College Algebra 13th Edition
Lial13th EditionCollege AlgebraISBN: 9780136881063당신이 사용하는 게 아니라요?교과서 변경
6장, 문제 69

Given A=[4231],B=[510237]A = \(\left\)[ \(\begin{matrix}\) 4 & -2 \\ 3 & 1 \(\end{matrix}\) \(\right\)], \(\quad\) B = \(\left\)[ \(\begin{matrix}\) 5 & 1 \\ 0 & -2 \\ 3 & 7 \(\end{matrix}\) \(\right\)] and C=[541036]C = \(\left\)[ \(\begin{matrix}\) -5 & 4 & 1 \\ 0 & 3 & 6 \(\end{matrix}\) \(\right\)] , find each product, if possible. See Examples 5–7. BA

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Identify the dimensions of matrices B and A. Since B is a 2x3 matrix, it has 2 rows and 3 columns. The matrix A's dimensions must be known or assumed to proceed. For the product BA to be defined, the number of columns in B must equal the number of rows in A.
Check the compatibility for multiplication BA. Specifically, if B is 2x3, then A must be a 3xN matrix (where N is any number) for the product BA to be possible. If A is not 3xN, then the product BA is not defined.
If the product BA is defined, determine the dimensions of the resulting matrix. The resulting matrix will have the number of rows of B and the number of columns of A, so it will be a 2xN matrix.
To compute the product BA, multiply each row of B by each column of A. This involves taking the dot product of the row vector from B with the column vector from A for each element in the resulting matrix.
Write the general formula for the element in the ith row and jth column of the product BA as: \[(BA)_{ij} = \sum_{k=1}^{3} B_{ik} \times A_{kj}\] where \(i\) ranges from 1 to 2 and \(j\) ranges from 1 to N.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Matrix Dimensions and Compatibility

Matrix multiplication is only defined when the number of columns in the first matrix equals the number of rows in the second. For example, if A is an m×n matrix and B is a p×q matrix, multiplication AB is possible only if n = p. Understanding this is essential to determine if the product BA exists.
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Introduction to Matrices

Matrix Multiplication Process

Matrix multiplication involves taking the dot product of rows from the first matrix with columns of the second. Each element in the product matrix is computed by summing the products of corresponding entries. This process results in a new matrix whose dimensions depend on the outer dimensions of the multiplied matrices.
추천 영상:
03:42
Finding Zeros & Their Multiplicity

Non-Commutativity of Matrix Multiplication

Unlike scalar multiplication, matrix multiplication is generally not commutative, meaning AB does not necessarily equal BA. Even if both products are defined, their results can differ. This concept is important when evaluating products like BA after AB.
추천 영상:
6:37
Permutations of Non-Distinct Objects