I have a matrix and I'm supposed to find the determinant. I chose to use the method of row reduction into echelon form and then multiplication across the diagonal. I row reduce the matrix but the answer I get is not the same as what my calculator says. I've gone over this 5 times now, and I can't find where I'm making a mistake. I feel like I'm missing some property of elementary operations but I dont see it.
After doing these row operations, I'm left with the matrix:
$3R_1+R_2$ to replace row 2.
$-2R_1+R_3$ to replace row 3.
$-4R_4+R_2$ to replace row 4.
If you multiply down the diagonal you get -48 but the answer is supposed to be 12 according to my calculator. What am I doing wrong?