Determinant e2×2-Diagonal Method Main Diagonal a11 a12 =111-0021 Secondary Diag a21 a22 Tongji University】 4/32Determinant 2 × 2—Diagonal Method . a11. a12. a21. a22. .        .        . = a11a22 . Main Diagonal −a12a21 . Secondary Diag (Tongji University) Linear Algebra 4 / 32