Eq. \ref{eq:6650345} is an initial equation. $$T = 1 / f \label{eq:6650345}$$ Multiply both sides of Eq. \ref{eq:6650345} by $$f$$; yields Eq. \ref{eq:2414344}. $$T f = 1 \label{eq:2414344}$$ Divide both sides of Eq. \ref{eq:2414344} by $$T$$; yields Eq. \ref{eq:5564581}. $$f = 1/T \label{eq:5564581}$$ Eq. \ref{eq:5564581} is one of the final equations.