Originally Posted by
thekrown Okay this doesn't make any sense. I have to find the inverse matrix by using a theorem in my textbook. This theorem uses the adjoint to find the inverse matrix.
Unfortunately it's a 4x4 matrix so it will take me a while to do but there's something that isn't right.
Here is the matrix A
1 3 1 1
2 5 2 2
1 3 8 9
1 3 2 2
My textbook has the answer inverse of A as
-4 3 0 -1
2 -1 0 0
-7 0 -1 8
6 0 1 -7
Okay, now I know how to do this. Let me know if I got this straight.
Step 1: find the matrix of minors, all 16 of them.
Step 2: find the cofactors according to sign charts
Step 3: transpose the cofactor matrix to obtain adjoint of A
Step 4: Find the determinant of the 4x4 matrix
Step 5: 1/det A * adjoint A = inverse matrix of A
If this is correct, can someone help me out finding minors of 4x4 matrices? I can do it for 3x3 but I have difficulty for 4x4, same goes for the determinants. I'm a little confused about the rules but I understand how it works in 3x3 matrices.
Thank you.