🎯
det(A) = ad − bc
For 2×2: Left diagonal product MINUS Right diagonal product
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SWAP · NEGATE · DIVIDE
Adjugate: swap a&d, negate b&c, then divide by det(A)
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det = 0 → NO inverse
If determinant is zero, the matrix is singular (no inverse exists)
✅
AA⁻¹ = I
A matrix times its inverse always equals the identity matrix
↘️
3×3: Left − Right
Copy col 1&2, multiply diagonals. Left sums MINUS Right sums
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Identity = [1 0 / 0 1]
1s on main diagonal, 0s elsewhere. Any size n×n works.