  The equipartition analysis yields estimates of the radius and energy of
synchrotron self-absorbed radio sources. Here we generalize this method to
relativistic off-axis viewed emitters. We find that the Lorentz factor $\Gamma$
and the viewing angle $\theta$ cannot be determined independently but become
degenerate along a trajectory of minimal energy solutions. The solutions are
divided into on-axis and off-axis branches with the former reproducing the
classical analysis. A relativistic source viewed off-axis can be disguised as
an apparent Newtonian one. Applying this method to radio observations of
several tidal disruption events (TDEs), we find that the radio flare of AT
2018hyz which was observed a few years after the optical discovery could have
been produced by a relativistic off-axis jet with kinetic energy of
$\sim10^{53}\,\rm erg$ that was launched around the time of discovery.
