[tex]\bf \textit{middle point of 2 points }\\ \quad \\
\begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
P&({{ 3}}\quad ,&{{ 5}})\quad
% (c,d)
Q&({{ c}}\quad ,&{{ d}})
\end{array}\quad
% coordinates of midpoint
\left(\cfrac{{{ x_2}} + {{ x_1}}}{2}\quad ,\quad \cfrac{{{ y_2}} + {{ y_1}}}{2} \right)=(-2,0)\\\\
-----------------------------\\\\
\left(\cfrac{{{ c}} + {{ 3}}}{2}\quad ,\quad \cfrac{{{ d}} + {{ 5}}}{2} \right)=(-2,0)M\implies
\begin{cases}
\cfrac{c+3}{2}=-2\\\\
\cfrac{d+5}{2}=0
\end{cases}[/tex]
if you solve those equations for "c" and "d" respectively, you'd get, well the Q point of c,d
