[tex]\text{The formula of the midpoint of a segment with the end points:}\\\\A(x_A;\ y_A)\ \text{and}\ B(x_B;\ y_B)\\\\M_{AB}=\left(\dfrac{x_A+x_B}{2};\ \dfrac{y_A+y_B}{2}\right)[/tex]
[tex]\text{We have:}\\A(16;\ 5)\to x_A=16;\ y_A=5\\B(28;\ -13)\to x_B=28;\ y_B=-13\\\\\text{substitute:}\\\\M_{AB}=\left(\dfrac{16+28}{2};\ \dfrac{5+(-13)}{2}\right)=\left(\dfrac{44}{2};\ \dfrac{-8}{2}\right)=(22;\ -4)[/tex]
