I used this: https://en.wikipedia.org/wiki/Laplace_expansion
In linear algebra, the Laplace expansion, named after Pierre-Simon Laplace, also called cofactor expansion, is an expression of the determinant of an n Ă n-matrix B as a weighted sum of minors, which are the determinants of some (n â 1) Ă (n â 1)-submatrices of B. Specifically, for every i, the Laplace expansion along the ith row is the equality...


reaction for more information.
