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Answers for “为什么在应用矩阵变换之前要将列向量重写为标准基向量的形式?”

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Rewriting a vector as a linear combination of standard basis vectors allows you to use the linearity of the transformation. Instead of computing the full matrix-vector product directly, you can apply the transformation to each basis vector separately (which corresponds to the columns of the matrix) and then combine the results using the original coefficients.

Conditions: The vectors are in R3R^3.; The coefficients are the coordinates of the vector relative to the standard basis.; A is linear: applying it preserves sums and scalar multiples.

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The missing middle column is [0−169]\begin{bmatrix} 0 \\ -16 \\ 9 \end{bmatrix}. This is obtained by applying the transformation A to the middle column of B, which is [023]\begin{bmatrix} 0 \\ 2 \\ 3 \end{bmatrix}.

Conditions: A and B are the specific 3x3 matrices shown in the video.; The method of column-wise composition is used.

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The j-th column of the composed matrix A∘BA \circ B is the image under A of the j-th column of B. To find a missing column, identify the corresponding column in B, treat it as an input vector, and apply the transformation A to it.

Conditions: A is a linear transformation represented by a matrix.; Columns are read as vectors in the domain of A.