Theorem: Delta lambda(theta = pi/2) - h/(m_e c) = 0 (Compton wavelength at 90 deg)

Theorem (Compton-perpendicular canonical): at scattering angle theta = pi/2, cos(pi/2) = 0, so Delta lambda = (h / m_e c)(1 - 0) = h / m_e c = lambda_C exactly - the Compton wavelength of the electron (lambda_C ≈ 2.43e-12 m = 2.43 pm).…