Midpoint formula
[tex](x_m,y_m)=(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})[/tex]
where (x1, y1) and (x2, y2) are two points and (xm, ym) are the coordinates of the midpoint between (x1, y1) and (x2, y2).
In this case, we want to find the coordinates of the midpoint between Y(0, -4b) and Z(-2a, 0). Substituting into the above formula:
[tex]\begin{gathered} (x_m,y_m)=(\frac{0+(-2a)}{2},\frac{-4b+0}{2}) \\ (x_m,y_m)=(\frac{-2a}{2},\frac{-4b}{2}) \\ (x_m,y_m)=(-a,-2b) \end{gathered}[/tex]
