The oblique incidence of a plane light wave on a cholesteric liquid crystal or a twisted nematic with a lead of a helix larger than the light wavelength is considered. The value of optical anisotropy is assumed to be arbitrary. The solution is obtained by the WKB method. The iteration procedure in powers of the ratio of the wavelength to the lead of a helix is developed. The results are compared with the exact solution for the case of normal incidence. Parameters of the wave transmitted through a cholesteric layer are calculated by means of Fresnel's formulas for the isotropic-anisotropic medium interface.