Answer
The midpoint of the line segment $~\overline{P_1P_2}~$ is: $(1, 4, \frac{9}{2})$
Work Step by Step
$P_1 = (-1,2,3)$
$P_2 = (3,6,6)$
We can find the midpoint between these two points:
$(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2} ,\frac{z_1+z_2}{2})$
$= (\frac{-1+3)}{2},\frac{2+6}{2} ,\frac{3+6}{2})$
$ = (1, 4, \frac{9}{2})$
The midpoint of the line segment $~\overline{P_1P_2}~$ is: $(1, 4, \frac{9}{2})$