Answer :
[tex]A(x_A;\ y_A);\ B(x_B;\ y_B)\\\\midpoint\ AB:\ S_{AB}\left(\frac{x_A+x_B}{2};\ \frac{y_A+y_B}{2}\right)\\\\P_1(3;-4);\ P_2(5;\ 4)\\\\S_{P_1P_2}\left(\frac{3+5}{2};\ \frac{-4+4}{2}\right)\to S_{P_1P_2}\left(\frac{8}{2};\ \frac{0}{2}\right)\to S_{P_1P_2}(4;\ 0)[/tex]
