The dispersion relation of waves in a cold magnetoplasma can be given in the form &Sgr;i=0 p Au(k) &ohgr;'=0, where &ohgr; is the frequency and the coefficients Ai are functions of the wave vector k. The group velocity Vg can be expressed as Vg=-&Sgr;i=0 p (∂Ai/∂k) &ohgr;i/ &Sgr;ii=0 piAi&ohgr;i-1. The equation is used for numerical studies of the slow and fast mode propagation in a one-ion plasma. The slow mode is always guided by the magnetostatic field B0, whereas the fast mode is guided only for frequencies in the 'whistler band'. The 'nose frequency' for the whistlers decreases as the angle ϑ=- (k, B0) increases.