which is negative for small angles (that is, near normal incidence), but changes sign at Brewster's angle, where θ i and θ t are complementary. Thus the phase shift δ p is 180° for small θ i but switches to 0° at Brewster's angle. Combining the complementarity with Snell's law yields ‍ θ i = arctan (1/ n) ‍ as Brewster's angle for dense-to-rare incidence.