- #1

- 112

- 13

$$p_e^2 \equiv \textbf{p}_e\cdot \textbf{p}_e = p_a^2+p_b^2+p_o^2 + 2\textbf{p}_a\cdot \textbf{p}_b - 2\textbf{p}_a\cdot \textbf{p}_0 - 2\textbf{p}_0\cdot \textbf{p}_b $$ $$= p_a^2+p_b^2+p_o^2 + 2p_ap_b\cos(\pi - \phi) - 2p_ap_0\cos \theta - 2p_bp_0\cos \theta$$

but then could not go any further. Am I misunderstanding the geometrical relationships of the vectors in Figure 5.1?