## Geometry: Common Core (15th Edition)

$K(1,1)$
use the midpoint formula $M_x=\frac{x_1+x_2}{2}$ substitute $5=\frac{9+x_2}{2}$ multiply both sides by 2 $5\times2=\frac{9+x_2}{2}\times2$ $10=9+x_2$ subtract 9 from each side $10-9=9+x_2-9$ simplify $1=x_2$ $M_y=\frac{y_1+y_2}{2}$ substitute $-2=\frac{-5+y_2}{2}$ multiply both sides by 2 $-2\times2=\frac{-5+y_2}{2}\times2$ $-4=-5+y_2$ add 5 to each side $-4+5=-5+y_2+5$ simplify $1=y_2$