since TU is the midsegment in the triangle, then T and U are both midpoints.
[tex]\bf ~~~~~~~~~~~~\textit{middle point of 2 points } \\\\ R(\stackrel{x_1}{0}~,~\stackrel{y_1}{2b})\qquad Q(\stackrel{x_2}{-2a}~,~\stackrel{y_2}{0}) \qquad \left(\cfrac{ x_2 + x_1}{2}~~~ ,~~~ \cfrac{ y_2 + y_1}{2} \right) \\\\\\ \stackrel{midpoint}{T}=\left( \cfrac{-2a+0}{2}~~,~~\cfrac{0+2b}{2} \right)\implies T=\left( \cfrac{-2a}{2}~,~\cfrac{2b}{2} \right) \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ ~\hfill T=(-a,b)~\hfill[/tex]
