v 7.11

n^{2} = ε = 1 + \frac{N e^{2}}{ε_{0} m_{e}} \sum_{i} \frac{f_{i}}{ω_{0 i}^{2} - ω^{2}}

${n^2= \varepsilon = 1+ \frac{Ne^2}{\varepsilon_0 m_e} \sum_i \frac{f_i}{\omega_{0i}^2 - \omega^2}}$

Error