I continue discussion on degenerate perturbation theory by discussing a specific example. This is one of the simplest systems to exhibit degeneracy - the two dimensional simple harmonic oscillator. I consider a perturbation of the form K x y - which actually leads to an exactly solvable problem. I discuss the effect of perturbation specifically for the first exited state, which is two fold degenerate in this case. I finally compare the result with the exact solution.
