Answer
\begin{array}{lclcl}
b_1=4&\\
b_2=6&\\
b_3=4&\\
b_4=6\\
\end{array}
Work Step by Step
Given $$\ \ \ b_n=5+\cos (n \pi), \ \ \ \ \ \ n= 1, 2,3, \dots
$$
So, we get
\begin{array}{|l|l|}\hline
& n& \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ b_n \\ \\ \hline
\text{First Term} & 1 & b_1=5+\cos (1 \pi)=5-1=4 \\ \\ \hline
\text{Second Term} & 2 & b_2=5+\cos (2 \pi)=5+1=6\\ \\ \hline
\text{Third Term} & 3 & b_3=5+\cos (3 \pi)=5-1=4\\ \\ \hline
\text{Fourth Term} & 4 & b_4=5+\cos (4 \pi)=5+1=6\\ \\ \hline
\end{array}
