Exercise 4.3.11

(a) The best line $x=1+4t$ gives the center point $\hat{b}=9$ at center time, $\hat{t}=2$.

(b) The first equation $\mathit{Cm}+D\sum <!--\; FUNCTION\; APPLICATION\; -->t_i=\sum b_i$ divided by $m$ gives $C+D\hat{t}=\hat{b}$. This shows: The best line goes through $\hat{b}$ at time $\hat{t}$.