Calculate det(1230012120121001)\det\begin{pmatrix} 1 & 2 & 3 & 0 \\ 0 & 1 & 2 & 1 \\ 2 & 0 & 1 & 2 \\ 1 & 0 & 0 & 1 \end{pmatrix}det1021210032100121 using cofactor expansion along the second column.
777
−7-7−7
141414
000