8.1: Appendix

error\(=\sum_{i=1}^{n}\left(x_{i}-\bar{X}\right)=0\)
\[
\begin{array}{c}
{\sum_{i=1}^{n} x_{i}-\sum_{i=1}^{n} \bar{X}=0} \\
{\sum_{i=1}^{n} x_{i}=\sum_{i=1}^{n} \bar{X}} \\
{\sum_{i=1}^{n} x_{i}=n \bar{X}} \\
{\sum_{i=1}^{n} x_{i}=\sum_{i=1}^{n} x_{i}}
\end{array}
\nonumber\]