Question

Please help me with math?

Answer 1

See the attachments.

Answer 2

\(A_{21}~~or~~E_{21}\)??

Answer 3

E21

Answer 4

@amistre64

Answer 5

You have to say what are you doing first, this is the second time I ask you about this. Why? because there is no information about your question. I know Gaussian process;I know cofactor matrices, but they are different. Gaussian use E1, E2, E3.... to eliminate the matrix A. Cofactor matrices use \(A_{12}~~A_{21}\) or else to find out the inverse matrix of A.
You use \(E_{21} \) notation which is soooo unfamiliar to me. I don't know how to answer. That's why I ask you to tag others whose knowledge is at higher level than I am to answer you