I am not sure I understood what you need.
\[
\frac {dP}{dr} = \frac {-(P+ \rho c^2) \nu'} {2} \tag { Oppenheimer & Volkoff}
\]
\frac {dP}{dr} = \frac {-(P+\pho c^2) \nu'} {2} \tag { Oppenheimer \& Volkoff}
I need to get these in one line, please someone write me the exact code for this , i also have other equations before it, that i need to align with this line
the lines upper to this equation is
\begin{equation}
\left.
\begin{aligned}
KP &= e^{-\lambda} \Big( \frac {\nu'}{r}+ \frac {1}{r^2}\Big)-\frac {1}{r^2} \\
KP &= e^{-\lambda} \Big(\frac {\nu ''}{2}-\frac {\lambda ' \nu '}{4} + \frac {(\nu')^2}{4} + \frac {\nu' -\lambda'}{2r}\Big) \\
K \rho c^2 &= e^{-\lambda}\Big (\frac {\lambda '}{r}-\frac {1}{r^2}\Big) +\frac {1}{r^2}
\end{aligned}
\right\} \tag{Tolman 1939}
\end{equation}