In the adj of ab how did 87 and 47 became -87 and -47??

Dear Student,
The question is incomplete. But it feels like you wanted to ask why adjoint of  $A_{(0,1) } and A_{(1,0) } is -A_{(0,1) } and A_{(1,0)}$  in a 2*2 matrix.
In Linear Algebra, adjoint of a square matrix is the transpose of the cofactor matrix. where cofactor of $A_{(i,j)}= (-1{)}^{i+j}{M}_{(i,j)}$. Therefore,
$$\begin{gathered} Given Matrix A =\left[\begin{array}{cc}a& b\\ c& d\end{array}\right] \\ So, Cofactor matrix = \left[\begin{array}{cc}d& -c\\ -b& a\end{array}\right] \\ Hence, \\ Adjoint = (Cofactor matrix{)}^T \\ = \left[\begin{array}{cc}d& -b\\ -c& a\end{array}\right] \end{gathered}$$

Thanks& Regards