$A$ is a 3 × 4 matrix, and $B$ is a matrix for which both $A'B$ and $BA'$ are defined. What is the order of $B$ ?

3 \times 4

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4 \times 3

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3 \times 3

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4 \times 4

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Show the answer and explanation

CorrectNot quiteAnswer A

Correct answer: A

Worth noting

4 × 3 is the order of $A'$ itself; matching it to $A'$ is what addition needs, not multiplication.

Ten questions from Matrices, at your own pace.

AAA is a 3 × 4 matrix, and BBB is a matrix for which both A′BA'BA′B and BA′BA'BA′ are defined. What is the order of BBB?