Generalized Laplace Method for Simple Determination of Kerr-Newman Black   Hole Horizon Radius
  In this work we present a generalized Laplace method for a formal, simple, quasi-classical, determination of the outer and inner horizon radius of Kerr-Newman black hole. We consider classical gravitational interaction between a thin, with homogeneously distributed mass and electric charge, spherical (black) shell and a probe particle. Also, we use relativistic equivalence principle. Finally we suppose that probe particle propagates radially to shell with speed of light while tangentially it rotates in common with shell, so that total energy of a probe particle equals zero. 
Vladan Pankovic, Sima Ciganovic, Jovan Ivanovic