Question

P(-9, -10) and Q(-9, 6) are the endpoints of a line segment. What is the midpoint M of that line segment?

Answer 1

The formula of the coordinates of a midpoint:

$M\left(\dfrac{x_1+x_2}{2};\ \dfrac{y_1+y_2}{2}\right)$

We have:

$P(-9,\ -10)\to x_1=-9,\ y_1=-10\\\\Q(-9,\ 6)\to x_2=-9,\ y_2=6$

Substitute:

$\dfrac{-9+(-9)}{2}=\dfrac{-18}{2}=-9\\\\\dfrac{-10+6}{2}=\dfrac{-4}{2}=-2$

Answer:  $M(-9,\ -2)$