**Exact and Approximate Solutions Describing Expansion of Relativistic Ideal Fluid**

**Abstract:**

Solutions of the relativistic hydrodynamical equations are studied, which describe expansion of the relativistic ideal fluid with linear equation of state
(EOS) p=ke. In case of the extremely stiff EOS (k=1) we present a method of generation of exact solutions; some special solutions are
obtained describing spherical and non-spherical expansion. For 0.2 < k < 1 we found a representation of spherically symmetric ultra-relativistic radial
outflow in a form of an asymptotic series in negative powers of radial variable. The representation is used to obtain solutions for radial outflow with
outgoing shock waves.