# How to tag an equation? [duplicate]

I am typing in texmaker but using \tag{} is not giving me the desired result. It shows an error. Here is sample

\textbf{Proof-} It is clear that $Inn(G)\subseteq Aut_U(G)$.
So we let  $\varphi \in Aut_U(G)$ i.e. $\varphi(g)=u^{-1}gu$ for some
$u\in U(\mathbb{Z}G)$\\
$\therefore$ $u=g^{-1}u\varphi(g) \tag{*}$.


Error says -

! Package amsmath Error: \tag not allowed here.
See the amsmath package documentation for explanation.
Type H <return> for immediate help....