Chapter 1 - Tools of Geometry - 1-7 Midpoint and Distance in the Coordinate Plane - Practice and Problem-Solving Exercises - Page 54: 21

$S(5.5,-13.5)$

Use the midpoint formula to find the x-coordinate. $M=\frac{x_1+x_2}{2}$ $5=\frac{x_1+4.5}{2}$ $5\times2=\frac{x_1+4.5}{2}\times2$ $10=x_1+4.5$ $10-4.5=x_1+4.5-4.5$ $5.5=x_1$ Use the midpoint formula to find the y-coordinate. $M=\frac{y_1+y_2}{2}$ $-8=\frac{y_1+(-2.5)}{2}$ $-8\times2=\frac{y_1-2.5}{2}\times2$ $-16=y_1-2.5$ $-16+2.5=y_1-2.5+2.5$ $-13.5=y_1$