Determinant of 1x1 Matrix

For a $1\times 1$ matrix, the determinant is $\det ([a])=a$

Proof

If $a=0$ we have $\det ([0])=0$ as det is linear if $a\ne 0$, we have $\det ([a])=\det (a[1])=a\det ([1])=a\ast 1$ as $\det (I)=1$ Therefore, forall a, we get $\det ([a])=a$