- The determinant of any identity matrix is always 1.
- If you switch the rows or columns of a matrix, its determinant stays the same.
- If you multiply a row (or column) of a matrix (call it A) by a number k, then the determinant of that matrix is k*det(A). For example, if $ A=\begin{bmatrix} 1 & 2 & 3\\ 2 & 3 & 5\\ 3 & 5 & 0\end{bmatrix} $
then det(A)=8. Thus you can conclude if you multiply the top row by 10 (call the resulting matrix B), then det(B)=10*det(A)=80. $ det\begin{pmatrix}10 & 20 & 30\\ 2 & 3 & 5\\ 3 & 5 & 0\end{pmatrix}=80 $
- If you transpose a matrix (ie turn the rows into columns, and columns into rows), the determinant stays the same.
- If you multiply matrices and take the determinant, the result is the same as taking the determinants, and then multiplying the determinants. $ det(A)*det(B)=det(A*B) $.
- It follows that det(A^{-1})=1/det(A).
- It also follows from the above statement that if a matrix $ B=S^{-1}AS $, then $ det(B)=det(S^{-1}AS)=det(S^{-1})*det(A)*det(S)=det(S)/det(S)*det(A)=det(A). $
