In this book, the finite difference, finite element and the root finding approximations i.e. Newton, Quasi Newton and Broyden methods has been presented. We also consider the finite difference/finite element hybrid method to solve the wave equation in Einstein and de Sitter space-time. The mathematical model of the Higgs Boson equation in de Sitter space-time has been presented as a chapter. Finally, the finite difference/finite element solution using Newton linearization method has been presented.