cofactors

Finding the determinant of a 2×2 matrix is easy: You just do the criss-cross multiplication, and subtract.
The process for 3×3 matrices, while a bit messier, is still pretty straightforward: You add repeats of the first and second columns to the end of the determinant, multiply along all the diagonals, and add and subtract according to the rule.
But for 4×4 s and bigger determinants, you have to drop back down to the smaller 2×2 and 3×3 determinants by using things called "minors" and "cofactors".
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