An engineer designs an icy, frictionless curved roadway for vehicles of mass \(m\) traveling at a constant speed along a horizontal circular path of radius \(R\). The surface of the roadway is banked at a constant angle \(\theta\) above the horizontal. In terms of \(R\), \(g\), and \(\theta\), which of the following expressions gives the ideal speed \(v\) at which a vehicle can negotiate the turn without slipping up or down the incline?