First of all, it should be stated that this conclusion is incorrect. If the determinant of matrix A is equal to zero, then its adjoint matrix is not necessarily zero, and its adjoint matrix A* may be zero or a matrix with rank = 1, depending on its rank. ..

Because the determinant of a =0, then r (a)

If r(A)=n- 1, then r(A*)= 1, and A* is not equal to 0;

If r (a)

If the above problem is changed to the determinant of adjoint matrix with A =0, then the conclusion is correct.

And the answers given by the two prawns upstairs are all wrong. The determinant of A is equal to zero, so how can the inverse matrix of A appear?