[en] Approximate analytic solutions are found in the most general formulation of the problem of incoherent radiative transfer in a one-dimensional medium of finite optical thickness for the model of complete frequency redistribution. The accuracy of these solutions increases with increasing thickness of the layer, with decreasing probability of photon survival, and with closer approach of the frequency to the line center. In the worst case their error is of the order of a few percent. These solutions are illustrated by the example of calculation of Ambartsumyan's Phi and Psi functions for Doppler and Lorentz profiles of the spectral line