A diffraction grating with a slit separation d is illuminated by a beam of monochromatic light of wavelength l. The diffracted beam is observed at an angle f relative to the incident direction. If the plane of the grating bisects the angle between the incident and diffracted beams, show that the mth maximum will be observed at an angle that satisfies the relation mλ = 2d sin (ф/2), with m = 0, ±1, ±2, . . . .