Lecture 4, homework problem 1. The solution uses positive K.$$hc/\lambda=KZ^2/n^2+m_ev^2/2=K/9+m_ev^2/2$$$$v=9.35*10^5 m/s$$
Shouldn't this be negative K?$$hc/\lambda=-KZ^2/n^2+m_ev^2/2=-K/9+m_ev^2/2$$$$v=1.39*10^6 m/s$$
Is positive K used because we are talking about the energy and velocity of the free electron instead of the bound electron?

Question

Lecture 4, homework problem 1.  The solution uses positive K.$$hc/\lambda=KZ^2/n^2+m_ev^2/2=K/9+m_ev^2/2$$$$v=9.35*10^5 m/s$$
Shouldn't this be negative K?$$hc/\lambda=-KZ^2/n^2+m_ev^2/2=-K/9+m_ev^2/2$$$$v=1.39*10^6 m/s$$
Is positive K used because we are talking about the energy and velocity of the free electron instead of the bound electron?

anonymous · Answer

THere I find a fishy thing too, the term that is $$\left( 1/nf ^{2} - 1/n i^{2} \right) $$ is expressed just as  1/nf ^{2} 

I cant understand why would they skip the initial n=1