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Year 10 · Patterns & Algebra

Matrix multiplication and determinants

A matrix is a grid of numbers. Add matching entries, scale every entry, or multiply rows by columns.

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How to do it

  1. Add: entry plus matching entry.
  2. Scalar: multiply every entry.
  3. Product: row of the first times column of the second. Determinant of [a b; c d] is ad − bc.

Worked example

What is the entry in row 2, column 1 of AB?
Row 2 of A times column 1 of B: (0)(-5) + (-3)(5) = -15.
Answer: -15

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AB and BA are usually different.

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