\frac{1}{E_{f}} − \frac{1}{E_{i}} = \frac{1}{m_{e}c^{2}} (1 − cos θ)

E_{f} ∼ E_{i} (\frac{2}{1 − v/c})

Lorentz factor γ = \frac{1}{\sqrt{1 − \frac{v^{2}}{c^{2}}}}