Chapter 3, Section 3.10, Figure 3.22

A straight-forward plot of the function H(θ) given in Eq.(3.129).

Plot[1/Sin[(θ °)/2]-2*Cos[θ °]-2,{θ,10,180},
 PlotRange->{{0,180},{-1,1}},Frame->True,
 AxesOrigin->{0,-1}]