Determinants, Orientation and Invertibility — Cheat sheet

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Core rule

det⁡(AB)=det⁡Adet⁡B\det(AB)=\det A\det B. Row swap: negate. Row scale: scale. Add a row multiple: unchanged. Triangular determinant: diagonal product.

Watch for

Determinants apply to square matrices. Magnitude measures volume scaling, not by itself numerical conditioning.