Question

could anybody explain thee last step of this proof?
where they say Aj1* = Aj1

Answer 1

what's the definition of cofactor?

Answer 2

Aij= (-1)i+j det Aij)

Answer 3

given a matrix, the co-factor of a specific row if found by "crossing off" that row
(and the column, for each column)
if we are crossing off the jth row of both matrix A and A*, and the only difference between the matrices is the jth row, it should be clear we get the same co-factor for both matrices (when expanding along the jth row)

Answer 4

thanks!