Determinants

⁦Work out 2 × 2 and 3 × 3 determinants, see what swapping rows does, and see how the determinant scales areas⁩.

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الدليل

The محدد ⁦is a number that belongs to a square matrix⁩. ⁦For order 2 it is ad − bc⁩: ⁦the product on the main diagonal minus the product on the other diagonal⁩.

⁦For order 3 expand along a row⁩: ⁦each entry times the determinant of what is left when its row and column are crossed out⁩. ⁦The signs go + − + along the row⁩. ⁦Forgetting the alternating signs is the common slip⁩.

⁦Swapping two rows changes the sign of the determinant⁩. ⁦A matrix as a transformation multiplies every area by the absolute value of its determinant⁩.

⁦Bars (vertical lines) mean the determinant, brackets mean the matrix⁩. ⁦Ask your child why it is a number, not a table⁩.