$\"\"$

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Multiply the matrix A(BC).

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Substitute matrices B and C. \ \

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$\"\"$

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Multiply columns by rows.

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$\"\"$

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$\"\"$

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$\"\"$

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Substitute matrix A

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$\"\"$

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Multiply columns by rows.

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$\"\"$

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$\"\"$

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$\"\"$

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Multiply the matrix (AB) C.

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$\"\"$

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Multiply columns by rows.

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$\"\"$ \ \

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$\"\"$

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$\"\"$

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Substitute matrix C \ \

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$\"\"$

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Multiply columns by rows.

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$\"\"$

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$\"\"$

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$\"\"$

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The solution of matrix A(BC) = (AB)C is True.

\