Determinant ●2×2—Diagonal1 ethod 1D20a 411a12 Secondary Diae do aa2 (Tongji University) 4/32Determinant 2 × 2—Diagonal Method . a11. a12. a21. a22. .        .        . = a11a22 . Main Diagonal −a12a21 . Secondary Diag (Tongji University) Linear Algebra 4 / 32