Chapter 1 - Tools of Geometry - 1-7 Midpoint and Distance in the Coordinate Plane - Practice and Problem-Solving Exercises - Page 54: 17

$S(5,-1)$

Use the midpoint formula to find the x-coordinate. $M=\frac{x_1+x_2}{2}$ $5=\frac{x_1+5}{2}$ $5\times2=\frac{x_1+5}{2}\times2$ $10=x_1+5$ $10-5=x_1+5-5$ $5=x_1$ Use the midpoint formula to find the y-coordinate. $M=\frac{y_1+y_2}{2}$ $-8=\frac{y_1+(-15)}{2}$ $-8\times2=\frac{y_1-15}{2}\times2$ $-16=y_1-15$ $-16+15=y_1-15+15$ $-1=y_1$