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I would like to know how exactly this works. I watched a khan academy video: "Multiplying matrices" but in this case he would've done B*A and had 2 columns, why does this one have 3 columns and 3 rows??

3 Answers 3

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the number of rows in the product is equal to the number of rows in the first factor and the number of columns in the product is equal to the number of columns in the second factor.

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    Gotcha, but I still don't know how I would multiply this... – 2017-02-02
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    I thought you said you looked at the khan academy video – 2017-02-02
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    https://www.khanacademy.org/math/precalculus/precalc-matrices/multiplying-matrices-by-matrices/v/multiplying-a-matrix-by-a-matrix – 2017-02-02
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    I am still confused on this.. – 2017-02-02
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    what is the confusion? – 2017-02-02
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Going off the video: your answer will be a $3 \times 3$ matrix. How can you tell this before you start doing the multiplication? Once you know that, follow the process that he starts at 2:35. For example, the upper-left entry is $$ 1 \cdot 6 + 2 \cdot (-2) = 2 $$

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    It would help if you explained exactly where you're getting confused – 2017-02-02
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A is 3 × 2 matrix.

B is 2 × 3 matrix.

Number of columns in A = Number of rows in B

So multiplication possible.

Resultant matrix C = Number of rows in A × Number of columns in B

We get C matrix 3 × 3.