Determinants and invertibility
With Aᵢⱼ formed by deleting row i and column j, cofactor expansion gives det A=Σⱼ(−1)ⁱ⁺ʲaᵢⱼdet Aᵢⱼ, starting from det[a]=a.
Key knowledge
With Aᵢⱼ formed by deleting row i and column j, cofactor expansion gives det A=Σⱼ(−1)ⁱ⁺ʲaᵢⱼdet Aᵢⱼ, starting from det[a]=a. It satisfies det(AB)=det A det B; A is invertible exactly when det A≠0.
Conditions and scope
- Use finite square matrices of one size over R or C; cofactor expansion uses any fixed row i.
- Nonzero determinant is an exact algebraic criterion, not a reliable floating-point singularity test.
Sources · 1
References
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Evidence and review
Appendix A.6 recursive cofactor construction and row expansion; Theorems A.6.1–A.6.2.
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