[tex]\begin{gathered} \text{mid point = (}\frac{x_1+x_2}{2},\frac{y_1+y_2}{2}\text{)} \\ (4,1)\text{ = (}\frac{2+x_2}{2},\frac{8+y_2}{2}\text{)} \\ \frac{2+x_2}{2}=4 \\ 2+x_2=8 \\ x_2=8-2 \\ x_2=6 \\ \\ \frac{8+y_2}{2}=1 \\ 8+y_2=2 \\ y_2=2-8 \\ y_2=-6 \\ B=(6,-6) \end{gathered}[/tex]
